Topics to be Learn

  • Introduction
  • Nervous Coordination
  • Nervous System in Hydra
  • Nervous System in Planaria (flatworm)
  • Neural tissue
  • Synapse
  • Transmission of nerve impulse along the axon
  • Human Nervous System
  • Sensory Receptors
  • Disorders of nervous system
  • Chemical Coordination
  • Endocrine system
  • Major endocrine glands

Control and Coordination in Plants and Animals:

  • Plants: Control and coordination achieved via chemical signals and various movements. Chemical signals used for coordination.
  • Animals: Complex control and coordination through electrical and chemical signals. Coordination via nervous system and endocrine system.

Nervous Systems in Different Animal Groups:

1. Hydra (Phylum: Cnidaria): 

  • Primitive nervous system with a nerve net.
  • Two nerve nets connected to epidermis and gastro-dermis.
  • No sensory organs, but scattered sensory cells.
  • Nerve impulses show no polarity, response throughout body.

2. Planaria (Flatworm) (Phylum: Platyhelminthes):  

  • Central Nervous System (CNS) on ventral side.  
  • Mass of cerebral ganglion resembling inverted U-shaped brain. 
  • Ventral Nerve Cords (VNC) interconnected by transfer nerves. 
  • Peripheral Nervous System (PNS) includes sensory cells.

3. Sponges (Phylum: Porifera): Lack nervous system.

4. Earthworm (Phylum: Annelida):

  • Ganglionated nervous system.
  • Position: Ventral, solid.
  • Composition: CNS, PNS, Sympathetic NS.

5. Cockroach (Phylum: Arthropoda):

  • Ganglionated nervous system.
  • Position: Ventral, solid.
  • Composition: CNS, PNS, ANS.

6. Human (Phylum: Chordata):

  • Non-ganglionated nervous system.
  • Position: Dorsal, hollow.
  • Composition: CNS, PNS, ANS. 

Neural Tissue:

  • Cells in Neural Tissue:
  • Neurons and Neuroglia (or glial cells).
  • Nerve: Bundle of axons; called nerve outside CNS and tract inside.

Types of Nerves:

  • Sensory Nerves: With sensory fibers.
  • Motor Nerves: With motor fibers.
  • Mixed Nerves: With both sensory and motor fibers.

Neurons/Nerve Cells:

  • Neuron: Structural and functional unit.
  • Multipolar Neuron: Three parts: cyton (cell body), dendron, and axon.

Grey Matter and White Matter:

  • Grey Matter: Darker part of CNS with cytons.
  • White Matter: Lighter part of CNS due to myelin sheath axons.

PNS Features: Cyton accumulation causes swelling on nerve, called ganglion.

Connective Tissue Layers in a Nerve:

  • Endoneurium: Covers each nerve fiber.
  • Perineurium: Covers nerve bundles.
  • Epineurium: Covers multiple nerve bundles forming a peripheral nerve.  

Neuroglial Cells:

  • More numerous than neurons.
  • Supporting cells of both Central Nervous System (CNS) and Peripheral Nervous System (PNS).
  • Neurilemma: Plasma membrane of Schwann cell.

Types of Neuroglial Cells:

CNS (Central Nervous System)

1. Oligodendrocytes: 

  • Form myelin sheath around central axons. 
  • Myelin sheath allows quick transmission of electrical impulses.

2. Microglia or Brain Macrophages: 

  • Small cells derived from monocytes. 
  • Act as macrophages, mediating immune response in CNS.

3. Astrocytes

  • Star-shaped and abundant in CNS.
  • Have varied roles including secretion and absorption of neurotransmitters, maintenance of blood-brain barrier (BBB), and regulation of electrical impulses transmission.

4. Ependymal Cells

  • Line ventricles and central canal with squamous or columnar epithelial cells.
  • Responsible for production and possibly circulation of cerebrospinal fluid (CSF) in brain.

PNS (Peripheral Nervous System)

1. Schwann Cells

  • Most abundant glial cells in PNS.
  • Produce myelin sheath around medullated nerves.

2. Satellite Cells

  • Support functions of neurons.

Synapse:
  • Microscopic gap between successive neurons.
  • Telodendrites of pre-synaptic neuron near dendrites of post-synaptic neuron.
  • Also known as synaptic cleft.
  • Filled with neurotransmitters like acetylcholine during nerve impulse transmission.
  • Motor end plate or neuromuscular junction when telodendria connect to muscle fiber.

Properties of Nerve Fibers: Excitability/Irritability, Conductivity, Stimulus (Subliminal & Supraliminal), Summation Effect, All or None Law, Refractory Period, Synaptic Delay, Synaptic Fatigue, Velocity.

Types of Synapses:
  • Electrical Synapse: Found in areas requiring rapid response like defense reflexes. 
  • Chemical Synapse: Found in neuromuscular junctions between motor neuron and muscle cell.

Components of a Typical Chemical Synapse:

  • Pre-synaptic Terminal
  • Synaptic Cleft
  • Post-synaptic Neuron

Transmission of Nerve Impulse Across a Synapse:
  • Occurs via neurotransmitters.
  • Action can be excitatory or inhibitory based on neurotransmitter type.
  • Acetylcholinesterase enzyme destroys neurotransmitter after transmission.
Transmission of Nerve Impulse Along the Axon:
  • Excitable neurons transmit impulse via changes in electrical charges across neuronal membrane.
  • External tissue fluid contains Na+ and K+ ions.
  • Sodium-potassium exchange pump involved.
  • Generation of nerve impulse occurs through depolarization.
  • Saltatory conduction in myelinated nerve fibers.

Steps in generation and conduction of nerve impuls


Human Nervous System:

Central Nervous System (CNS):

Location:
  • Brain enclosed within cranial skull.
  • Spinal cord lies in vertebral canal of vertebral column.

Meninges of CNS: Three protective membranes covering brain and spinal cord.

Types:
Dura Mater:
  • Outermost, tough, fibrous.
  • Attached to inner side of cranium.
Arachnoid Mater:
  • Middle, thin, vascular.
  • Nutritive function, protects brain.
Pia Mater:
  • Innermost, highly vascular, thin.
  • Lies in contact with CNS, nutritive function.
Spaces:
  • Subdural Space: Between dura mater and arachnoid mater; filled with serous fluid.
  • Sub-arachnoidal Space: Between arachnoid mater and pia mater; filled with cerebrospinal fluid (CSF).

CSF (Cerebrospinal Fluid):
  • Composition: Lymph-like extracellular fluid, Specific gravity: 1.005, Present in and around CNS.
  • Secretion: By pia mater, choroid plexuses, and ependymal cells lining brain ventricles and spinal cord central canal.

Functions of Meninges and CSF:

  • Shock absorption, protection, prevention of desiccation.
  • Maintaining constant pressure inside and outside CNS.
  • Exchange of nutrients and wastes between blood and brain tissue.
  • Supply of oxygen to the brain.

The Human Brain:

  • Encephalology:Study of all aspects of the brain.
  • Division:Divided into three main parts: 1. Forebrain, 2. Midbrain 3. Hindbrain

Weight and Volume:

  • About 1300-1400g in weight. 
  • Volume ranges from 1300-1500cc.

Parts of the Brain:

1. Forebrain:

  • Cerebrum (Telencephalon) and Diencephalon (Thalamencephalon).
  • Underdeveloped olfactory lobes (Rhinencephalon) in anterior region.

2. Midbrain:

  • Consists of Corpora Quadrigemina and Crura Cerebri.

3. Hindbrain:

  • Cerebellum (Metencephalon) and Brain Stem.
  • Divided into Pons Varolii and Medulla Oblongata (Myelencephalon). 

Functional Areas of Cerebrum:

Sensory Area:
  • Receives sensory inputs, analyzed within.
  • Sensory speech area (Wernicke’s area) located in parietal lobe.
Association Area:
  • Processes, analyzes, and stores information.
  • Responsible for reasoning, will, understanding, memory, etc.
Motor Area:
  • Located in frontal lobe, anterior to premotor area.
  • Broca’s area (Motor speech area) controls speech movements, situated just above lateral sulcus.

Forebrain (Prosencephalon) and its Parts:

(i) Olfactory Lobes (Rhinencephalon):

  • Paired, small bodies in forebrain.
  • Consists of Olfactory bulbs and olfactory tracts.
  • Function: Sense of smell.

(ii) Cerebrum (Telencephalon) - 85% of Brain:

Structure Associated:
  • Corpus Callosum: Band connecting two hemispheres.
  • Pallium: Roof of brain.
  • Corpora Striata: Ventrolateral walls.
Peculiarities:
  • Divided by cerebral fissure into two hemispheres.
  • Outer cortex, inner medulla.
  • Gyri (ridges) and sulci (depressions).
  • Three deep sulci: Central, lateral, and parieto-occipital.
  • Four lobes: Anterior frontal, middle parietal, posterior occipital, and lateral temporal.
Functions:
  • Controls voluntary activities.
  • Perceives sensory stimuli (vision, taste, smell, sound, touch, speech).
  • Center for memory, willpower, intelligence, reasoning, learning.
  • Regulates emotions, thoughts, feelings, pain, pleasure, etc.
  • Controls micturition, defecation, weeping, laughing, etc.

(iii) Diencephalon (Thalamencephalon):

Structure Associated:
  • Epithalamus: Roof with anterior choroid plexus.
  • Thalami; Reticular Activating System (RAS) in thalami.
  • Hypothalamus: Floor of diencephalon.
Peculiarities:
  • Below corpus callosum, above midbrain.
  • Epithalamus with pineal body attached to pineal stalk.
  • Habenular commissure connects thalami.
  • Pituitary gland attached by infundibular stalk.
Functions:
  • Acts as relay center for motor and sensory impulses between spinal cord, brainstem, and cerebral cortex.
  • Homeostasis center and higher center of autonomous nervous system.
  • Hypothalamic nuclei secrete neurohormones influencing pituitary gland.
  • Regulates heartbeats, blood pressure, water balance.
  • Anterior choroid plexus secretes cerebrospinal fluid.
  • Controls involuntary functions like hunger, thirst, temperature regulation, emotions, etc.

Midbrain (Mesencephalon) and its Parts:

(i) Corpora Quadrigemina:

Peculiarities: Two pairs of lobes:
  • Superior Colliculi: Receives optic nerves.
  • Inferior Colliculi: Receives auditory nerves.
Functions:
  • Control and coordination of eye movement and head movement.
  • Control and coordination of auditory reflexes.
(ii) Crura Cerebri
  • Structure Associated: Connection of cerebrum to cerebellum.

Hindbrain (Rhombencephalon) and its Parts:

(i) Cerebellum (Metencephalon) - 11% of Brain, Second Largest Region:

Structure Associated:
  • Arbor Vitae: Tree-like processes of inner white matter into outer grey matter. 
Peculiarities:
  • Posterior most part.
  • Three lobes: Median vermis, two lateral cerebellar hemispheres.
Functions:
  • Primary center for control of equilibrium, posture, balancing, and orientation.
  • Regulation of neuromuscular activities.
  • Coordination of walking, running, speaking, etc.

(ii) Pons Varolii:

  • Nerve fibers forming bridges between cerebrum and medulla oblongata.
  • Outer white and inner grey matter; nerve fibers cross over.
Functions:
  • Coordinates activities of two cerebellar hemispheres.
  • Nerve fibers cross over, allowing right brain control over left body and vice versa.
  • Controls consciousness and breathing (breathing center).

(iii) Medulla Oblongata (Myelencephalon):

  • Posteriormost part, continues as spinal cord.
  • Outer white and inner grey matter; posterior choroid plexus.
  • Cranial nerves arise from medulla.
Functions:
  • Controls involuntary activities: heartbeats, respiration, vasomotor activities.
  • Regulates peristalsis and reflex actions like coughing, sneezing, swallowing.
  • Essential for vital functions of the body. 

Ventricles of Brain:
  • Cavities present in different parts of the brain.
  • Four ventricles in the human brain, all interconnected.
  • Filled with cerebrospinal fluid.
  • Paracoel or lateral ventricles I and II inside cerebral hemispheres.
  • Ventricle III in diencephalon, connected to lateral ventricles via foramen of Monro.

Important Terms Associated with Brain:

  • Corpus Callosum: Transverse band connecting right and left cerebral hemispheres.
  • Cerebral Cortex: Outer surface of cerebrum, composed of grey matter.
  • Cerebral Medulla: Inner part composed of white matter.
  • Gyri and Sulci: Elevations and depressions on cerebrum's surface.
  • Central Sulcus: Between frontal and parietal lobes.
  • Parieto-occipital Sulcus: Between parietal and occipital lobes.
  • Lateral or Sylvian Sulcus: Between temporal, frontal, and parietal lobes.
  • Insula: Folded lobe within lateral sulcus.
  • Foramen of Monroe: Opening connecting lateral ventricles with third ventricle.
  • Pineal Gland: Produces hormones melatonin and serotonin.
  • Habenular Commissure: Connects two thalami.
  • RAS (Reticular Activating System): Transmits sensory impulses to cerebrum, located in thalami.
  • Aqueduct of Sylvius or Iter: Connection between third and fourth ventricle.
  • Limbic System: Neuronal circuit for emotions, memory.
  • Optic Chiasma: Crossing of optic nerves.
  • Corpora Quadrigemina: Involved in visual and auditory reflexes.
  • Crura Cerebri: Thick fibrous tracks in midbrain.
  • Red Nucleus: Controls posture, muscle tone, motor coordination.
  • Pons Varolii: Rounded bulge on brainstem.
  • Brain Stem: Midbrain, pons, and medulla.
  • Arbor Vitae: White matter pattern resembling a branched tree.
  • Cerebellar Peduncles: Nerve bundles connecting cerebellum to CNS.
  • Foramina of Luschka and Magendie: Apertures on posterior choroid plexus.

Spinal Cord:
  • Part of central nervous system, extending from the brain's medulla oblongata.
  • Lies within neural canal of vertebral column, surrounded by three meninges.
  • Externally appears as long cylindrical rod, 42 to 45 cm long, 2.0 to 2.5 cm broad.
  • Conus Medullaris: Terminal nervous part of spinal cord.
  • Filum Terminale: Thread-like non-nervous extension. 31 pairs of spinal nerves arise from lateral sides.
  • Cauda Equina: Filum terminale with some spinal nerves, resembling a horse-tail.

Transverse Section (T.S.) of Spinal Cord:

  • Deep, narrow dorsal fissure and broad ventral fissure.
  • Inner grey matter is H-shaped, surrounded by outer white matter.
  • Grey matter divisible into six horns: dorsal, lateral, and ventral.
  • White matter divisible into six columns or funiculi: dorsal, lateral, and ventral.
  • Dorsal and ventral horns extend as dorsal and ventral roots.
  • Dorsal root has dorsal root ganglion (sensory neurons).
  • Interneurons lie inside grey matter.
  • White matter consists of myelinated nerve fiber bundles (ascending and descending tracts).

Functions:

  • Main center for reflex actions.
  • Provides pathway for sensory and motor impulses conduction.

Peripheral Nervous System (PNS): Connects central nervous system to body parts with receptors and effectors.
 
Two Types of Peripheral Nerves:
  • Cranial Nerves: Arise from brain.
  • Spinal Nerves: Arise from spinal cord.

Cranial Nerves - Nature and Functions:

  • Developed from brain in all amniotes (reptiles, birds, mammals).
  • 12 pairs originating from or terminating into the brain.
  • Classified as sensory, motor, or mixed nerves based on function.

Spinal Nerves: Thirty-one pairs originating from spinal cord.

 Formation of a Typical Spinal Nerve:

  • Formed inside neural canal of vertebral column.
  • Dorsal sensory and ventral motor nerves form mixed spinal nerve.
  • Upon emergence from vertebral column, shows three branches: Ramus dorsalis, Ramus ventralis, Ramus communicans.

Reflex Action: Quick, automatic, involuntary response to stimuli.

Reflex Arc:
  • Structural or functional unit of reflex action.
  • Components: Receptor organ, sensory neuron, association neuron, motor neuron, effector organ.
Types of Reflexes:
  • Based on location: Somatic (skeletal muscles) and Visceral (organs).
  • Based on neurons involved: Monosynaptic (one sensory, one motor) and Polysynaptic (more than two neurons).
  • Based on inheritance: Unconditional (inborn) and Conditional (acquired).
  • Based on control: Cranial (brain-controlled), Spinal (through spinal cord).

Autonomic Nervous System (ANS): Divided into Somatic (voluntary muscles) and Autonomic (involuntary organs, smooth muscles).
Sympathetic Nervous System (SNS):
  • Thoraco-lumbar outflow.
  • 22 pairs of ganglia near vertebral column.
  • Postganglionic fibers produce adrenaline (adrenergic fibers).
  • Functions in emergencies (fight, flight, fright).
Parasympathetic Nervous System (PNS):
  • Cranio-sacral outflow.
  • Ganglia near or within effector organs.
  • Postganglionic fibers produce acetylcholine (cholinergic fibers).
  • Counteracts sympathetic effects, maintains homeostasis.
Comparison between SNS and PNS:
  • Organ/Region: SNS Effect / PNS Effect
  • Heartbeat: Increases / Decreases
  • Blood vessels: Constricts / Dilates
  • Arterial B.P.: Increases / Decreases
  • Pupil of Eye: Dilates / Constricts
  • Gastrointestinal movements: Retards peristalsis / Accelerates peristalsis
  • Urinary bladder: Relaxes / Contracts

Sensory Receptors:Specialized structures modified to receive stimuli from external or internal environment.

Types of Exteroceptors and Interoceptors:

Exteroceptors (Receive external stimuli):
  • Phonoreceptors: Internal Ear (organ of corti) - Sound reception.
  • Statoreceptors: Internal Ear (semicircular canals) - Maintain balance and equilibrium.
  • Photoreceptors: Retina of Eye - Vision.
  • Thermoreceptors: Skin - Sense heat (caloriceptors) and cold (trigidocetptors).
  • Mechanoreceptors: Skin - Sensitive to touch, pain, pressure, etc.
  • Chemoreceptors: (i) Gustatoreceptors: Taste buds of tongue. (ii) Olfactory receptors: Olfactory Epithelium of Nose.
Interoceptors (Receive stimuli from within the body):
  • Enteroceptors: Internal body organs - Sensitivity to hunger, thirst, pain, etc.
  • Proprioceptors: Joints, muscles, tendons - Detect changes in movement, pain, tension, vibrations.
  • Baroreceptors: Present in walls of atria, venae cavae, aortic arch, carotid sinus - Sense changes in blood pressure.

Eye Anatomy:
  • Location: Eyes are sensory organs of vision located in the skull's orbit.
Structure: 
  • Each eye is spherical, called an eyeball, with three layers:
  • Sclera: Outer layer of dense connective tissue with a transparent cornea at the front.
  • Choroid: Middle layer containing blood vessels, thick anteriorly forming the ciliary body.
  • Retina: Innermost layer consisting of ganglion cells, bipolar cells, and photoreceptor cells sensitive to light. 

Photoreceptor Cells:

  • Two types: rods and cones containing light-sensitive proteins.
  • Rhodopsin: Found in rods, derived from vitamin A.
  • Iodopsin: Found in cones.
  • Function: Cones responsible for daylight and color vision, while rods function in dim light.

Optic Nerve and Blind Spot:

  • Optic Nerve: Leaves the eye slightly away from the median posterior pole.
  • Blind Spot: Area where optic nerve exits, devoid of rods and cones.
  • Macula Lutea: Yellow pigmented spot lateral to the blind spot.
  • Fovea: Thinned out portion of retina with densely packed cones, providing high visual acuity.

Generation of Image:

  • Light rays pass through conjunctiva, cornea, pupil, lens, and focus on the retina to form an image.
  • Nerve impulses analyzed in the visual area of cerebrum, leading to image recognition. 

Mechanism of Vision:

1. Nerve impulse transmitted via optic nerve to the brain.
2. Impulses converge and leave via the optic nerve's axons.
3. Transmitted to ganglion cells, then to bipolar nerve cells.
4. Stimulate rod and cone cells, generating nerve impulses.
5. Light-sensitive pigments break up by specific wavelength of light.
6. Light falls on rod and cone cells in retina.
7. Changes in retina occur when light rays fall on it.
8. Brain cells in the visual area of cerebrum perceive the image. 

Ear Anatomy:
  • Functions: Hearing and body equilibrium.
  • Divisions: External ear, middle ear, and inner ear.

1. External Ear:

  • Components: Ear pinna, auditory canal, and tympanic membrane.
  • Ear Pinna: Immovable part supported by elastic cartilage, collects sound waves.
  • Auditory Canal: Transfers sound waves to the tympanic membrane (eardrum).

2. Middle Ear:

  • Consists of malleus, incus, and stapes (ossicles).
  • Ossicles: Transmit sound waves from the auditory canal to the inner ear.
  • Eustachian Tube: Connects the middle ear to the pharynx, equalizes air pressure.

3. Inner Ear:

  • Structure: Fluid-filled labyrinth with bony and membranous parts.
  • Bony Labyrinth: Contains membranous labyrinth filled with endolymph fluid.
  • Membranes: Cochlea, Reissner’s membrane, and basilar membranes.
  • Cochlea: Contains the organ of Corti with hair cells acting as auditory receptors.
  • Vestibular Apparatus: Includes semicircular canals and otolith organ (sacculus and utriculus) responsible for body posture and balance.

Mechanism of Hearing: 

  • Sound waves received by the ear pinna.
  • Vibrations transmitted through the eardrum and ossicles to the endolymph in the cochlea.
  • Endolymph waves induce ripples in the basilar membrane.
  • Movement of basilar membrane causes hair cells to press against the tectorial membrane.
  • Generates nerve impulse in afferent neurons, sent to the brain via the auditory nerve.
  • Auditory cortex decodes the sound.

Disorders of the Nervous System:

Psychological Disorders: Also known as mental disorders, these conditions affect mood, thinking, or behavior.

Major categories include:

  • Intellectual disability (formerly known as mental retardation)
  • Autism spectrum disorder
  • Bipolar disorder
  • Depression
  • Anxiety disorder
  • ADHD (Attention Deficit Hyperactivity Disorder)
  • Stress-related disorders.

Parkinson’s Disease:

  • Caused by degeneration of dopamine-producing neurons in the CNS.
  • Symptoms develop gradually and include tremors, stiffness, difficulty in walking, and problems with balance and coordination.

Alzheimer’s Disease:

  • Most common form of dementia, with incidence increasing with age.
  • Symptoms involve loss of cognitive functioning, such as thinking, remembering, reasoning, and behavioral abilities, significantly impacting daily life and activities.

Chemical Coordination

Types of Cells Communication:
  • Autocrines: Cells stimulate themselves.
  • Paracrines: Cells stimulate neighboring cells.
  • Endocrines: Cells stimulate distant cells.
  • Pheromones: Cells/Organs stimulate other organisms.

Endocrine System:

  • Controls body activities through chemical messengers called hormones.
  • Endocrine glands are ductless glands that secrete hormones directly into the bloodstream.
  • Hormones regulate target tissues/organs with excitatory or inhibitory effects.

Main Endocrine Glands: Pituitary (hypophysis), Hypothalamus, Thyroid, Parathyroid, Adrenal (suprarenal), Islets of Langerhans in pancreas, Endocrine parts of gonads (testis and ovary), Pineal gland and thymus are also endocrine glands but of less importance.

Properties of Hormones:

  • Act as chemical messengers in low concentrations.
  • Can inhibit, stimulate, or modify specific processes.
  • Hypersecretion or hyposecretion leads to disorders.
  • Metabolized after function and excreted through urine.

Mechanism of Hormone Action:

  • Released in small quantities.
  • Bind to hormone receptors on target organs/cells.
  • Hormone receptors can be on cell membrane or intracellular.
  • Forms hormone-receptor complex leading to biochemical changes in target tissue.

Mode of Hormone Action:

  • Through Membrane Receptors: Non-lipid soluble hormones bind to specific receptors on cell membrane, causing the release of enzymes like adenylate cyclase and cyclic AMP as a second messenger.
  • Through Intracellular Receptors: Lipid-soluble hormones pass through plasma membrane, bind to intracellular receptor proteins, form hormone-receptor complex, enter nucleus, and bind to DNA's regulatory site.


Major Endocrine Glands

Hypothalamus:

  • Ectodermal in origin, forms floor of diencephalon.
  • Maintains homeostasis, controls pituitary gland via releasing and inhibiting hormones.
  • All hormones are peptide hormones.

Hormones of Hypothalamus:

1. Somatotropin/GHRF
2. Somatostatin/GHRIF
3. Adrenocorticotropin Releasing Hormone
4. Thyrotropin Releasing Factor
5. Gonadotropin Releasing Hormone (GnRH)
6. Prolactin Inhibiting Hormone (Prolactostatin)
7. Gastrin Releasing Peptide (GRP)
8. Gastric Inhibitory Polypeptide (GIP)

Pituitary Gland (Hypophysis):

  • Pea-sized reddish-grey gland below hypothalamus, controls other glands.
  • Anterior lobe (Adenohypophysis), posterior lobe (Neurohypophysis), and intermediate lobe (Pars intermedia).
  • Anterior lobe secretory, connected to hypothalamus by portal system.
  • Posterior lobe attached to hypothalamus by infundibular stalk, stores ADH and oxytocin.

Parts of Pituitary Gland:

 1. Adenohypophysis (Anterior lobe):

  • Largest lobe, developed from Rathke’s pouch.
  • Pars tuberalis, pars distalis, and pars intermedia.
  • Pars distalis secretes GH, TSH, ACTH, LTH, and GTH.
2. Neurohypophysis (Posterior lobe):
  • Smaller, attached to hypothalamus by infundibular stalk.
  • Contains pars nervosa, acts as neurohaemal organ, stores ADH and oxytocin.

Hypothalamo-Hypophyseal Portal System:

  • Connects hypothalamus and pituitary gland.
  • Hormones secreted by hypothalamus reach pituitary gland through this system.

Hormones of Pituitary and Their Role

1. Somatotropin or Somatotropic Hormone (STH) or Growth Hormone (GH):

  • Secreted by acidophils of adenohypophysis (Somatotropes).
  • Regulated by hypothalamus GHRF and GHIF or somatostatin.
  • Stimulates general body growth.
  • Disorders: Dwarfism (hyposecretion), Gigantism (hypersecretion), Acromegaly (hypersecretion).

2. Thyrotropin or Thyroid Stimulating Hormone (TSH):

  • Secreted by basophils of adenohypophysis (Thyrotropes).
  • Regulated by TRF from hypothalamus.
  • Stimulates thyroid gland for thyroxine formation.
  • Disorders: Thyroid atrophy (hyposecretion), Increased BMR (hypersecretion).

3. Corticotropin or Adrenocorticotropic Hormone (ACTH):

  • Secreted by basophils called corticotrophs.
  • Regulated by CRF from hypothalamus.
  • Stimulates adrenal cortex for glucocorticoids and mineralocorticoids.
  • Disorders: Rheumatoid arthritis, Addison’s disease (hyposecretion), Cushing’s disease (hypersecretion).

4. Follicle Stimulating Hormone (FSH):

  • Secreted by basophils.
  • Regulated by gonadotropin releasing factors from hypothalamus.
  • Stimulates ovary germinal epithelium and spermatogenesis.
  • Disorders: Infertility.

5. Luteinizing Hormone (LH in females):

  • Secreted by basophils.
  • Regulated by negative feedback between LH and progesterone.
  • Stimulates ovulation, corpus luteum formation.
  • Disorders: Infertility.

6. Interstitial Cell Stimulating Hormone (ICSH in males):

  • Secreted by basophils.
  • Regulated by negative feedback between ICSH and testosterone.
  • Stimulates Leydig cells for testosterone.
  • Function: Development of secondary sexual characteristics.

7. Luteotropic Hormone or Prolactin (LTH or PL):

  • Secreted by acidophils of adenohypophysis.
  • Regulated by PRF and PIF from hypothalamus.
  • Functions: Mammary gland development, milk secretion, corpus luteum maintenance.

8. Melanocyte Stimulating Hormone (MSH):

  • Secreted by pars intermedia.
  • Regulated by hypothalamic melanostatin.
  • Stimulates melanocytes for melanin synthesis, skin darkening.

9. Antidiuretic Hormone (ADH or Vasopressin):

  • Secreted by hypothalamic neurons.
  • Regulated by blood osmotic pressure.
  • Functions: Increases kidney permeability, reduces urine output, increases blood pressure.

10. Birth Hormone (Oxytocin):

  • Secreted during childbirth.
  • Functions: Uterine contractions, milk ejection, sperm ascent, muscle contractions in various organs.

11. Coherin: Function: Induces contractions of jejunum.


Pineal Gland:
  • Given off from the roof of diencephalon.
  • Located between the cerebral hemispheres.
  • Sensitive to light signals.
  • Secretes melatonin, the "sleep hormone".

Thyroid Gland:

  • Largest endocrine gland with two lobes connected by isthmus.
  • Internal structure: Follicles composed of cuboidal epithelium filled with gelatinous colloid.
  • Follicular cells secrete thyroxine (T4) and triiodothyronine (T3).
  • Parafollicular cells produce thyrocalcitonin. 

Formation of T3 and T4:

  • Thyroxine synthesized by attaching iodine to tyrosine.
  • T1 and T2 molecules combine to form colloidal mass, further metabolized to T3 and T4.

Functions of Thyroid Hormones:

  • Regulation of basal metabolic rate.
  • Stimulation of protein synthesis and tissue growth.
  • Calorigenic effect for heat production.
  • Increase action of neurotransmitters.
  • Support RBC production and electrolyte balance.
  • Regulation of reproductive cycles.
  • Thyrocalcitonin regulates calcium metabolism.

Functional Disorders of Thyroid Gland:

  • Hypothyroidism: Deficient thyroxine secretion causing cretinism (in children) and myxedema (in adults).
  • Hyperthyroidism: Excessive thyroxine secretion causing Grave's disease with symptoms like exophthalmos.
  • Simple Goitre: Enlargement of thyroid gland due to iodine deficiency, preventable by iodized salt.

Parathyroid Gland:
  • Situated on the posterior surface of thyroid gland lobes.
  • Consists of 2 pairs: superior and inferior parathyroid glands.
  • Cells arranged in a compact mass. 

Hormones:

  • Secretes parathormone (PTH) or Collip's hormone.
  • Regulates calcium and phosphate balance, acting as a hypercalcemic hormone.
  • Stimulates osteoclasts for bone resorption.
  • Antagonistic to calcitonin.

Disorders:

  • Hyposecretion causes parathyroid tetany, increasing nerve and muscle excitability.
  • Hypersecretion leads to osteoporosis due to excessive calcium absorption from bones.

Thymus Gland:

  • Located in the upper thorax behind the sternum.
  • Prominent at birth but gradually atrophies in adulthood due to sex hormones.

Functions:

  • Secretes thymosin.
  • Plays a vital role in immune system development by maturing T-lymphocytes.

Adrenal Gland/Suprarenal Gland:

  • Dual origin from mesoderm and ectoderm.
  • Located on the upper border of each kidney.
  • Small, conical yellowish glands with outer cortex and inner medulla.

Adrenal Cortex (Outer):

  • Derived from embryonic mesoderm.
  • Secretes corticoids, including mineralocorticoids and glucocorticoids.

Three Concentric Regions of Adrenal Cortex:

1. Zona glomerulosa (Outer Thin Cortex):
  • Secretes mineralocorticoids like aldosterone.
  • Regulates sodium and potassium ion concentration, maintaining salt-water balance, blood volume, and pressure.
2. Zona fasciculata (Middle Thick Cortex):
  • Produces glucocorticoids like cortisol.
  • Regulates carbohydrate, protein, and lipid metabolism.
  • Prepares the body for emergencies and has immunosuppressive effects.
3. Zona reticularis (Inner Thin Cortex):
  • Produces sex corticoids (gonadocorticoids) like androgens and estradiols.
  • Role in development and maintenance of external sex characters.

Adrenal Medulla (Inner):

  • Derived from embryonic ectoderm.
  • Secretes adrenaline (epinephrine) and noradrenaline (norepinephrine).
  • Adrenaline: Emergency hormone for fight, flight, and fright responses.
  • Noradrenaline: Regulates blood pressure by acting as a vasoconstrictor.

Disorders related to Adrenal Cortex:

  • Hyposecretion: Addison’s disease due to low levels of mineralocorticoids and glucocorticoids, causing symptoms like low blood sugar, weight loss, weakness, and nausea.
  • Hypersecretion: Cushing’s disease due to excessive glucocorticoid secretion, leading to high blood sugar, obesity, hypertension, and muscle wasting.

Pancreas:
  • Develops from endoderm.
  • Heterocrine gland: Exocrine part (pancreatic acini) secretes digestive enzymes, while endocrine part (Islets of Langerhans) secretes hormones.
Islets of Langerhans contain four types of cells:
  • Alpha (α) cells: Secrete glucagon, a hyperglycemic hormone.
  • Beta (β) cells: Secrete insulin, a hypoglycemic hormone.
  • Delta (δ) cells: Secrete somatostatin, which inhibits glucagon and insulin secretion.
  • PP cells or F cells: Secrete pancreatic polypeptide (PP), inhibiting pancreatic juice release.
Disorder: Diabetes mellitus, characterized by hyperglycemia due to underactivity of Beta cells.
  • Type-1 diabetes (Insulin-dependent diabetes mellitus): Results from decreased insulin secretion.
  • Type-2 diabetes (Non-insulin-dependent diabetes mellitus): Results from insulin resistance.

Gonads:
1. Ovaries:
  • Produce hormones:
  • Estrogen: Secreted by developing follicles, responsible for female secondary sexual characteristics.
  • Progesterone: Secreted by corpus luteum after ovulation, prepares uterus for implantation, and inhibits uterine contractions during pregnancy.
  • Relaxin: Secreted by corpus luteum, relaxes cervix and pelvic ligaments during pregnancy.
  • Inhibin: Secreted by corpus luteum, inhibits FSH and GnRH production.
2. Testes:
  • Secrete male sex hormone testosterone.
  • Produced by Leydig cells in response to luteinizing hormone (LH).
  • Responsible for male secondary sexual characteristics like facial hair, deep voice, etc.

Placenta:
  • Temporary endocrine source in pregnant women for material exchange. 
  • Secretes hormones: estrogen, progesterone, HCG, and human placental progesterone.

Diffused Endocrine Glands:

  • Gastrointestinal Tract: Hormones: Gastrin, Secretin, Cholecystokinin (CCK)/Pancreozymin (PZ), Entero-gastrone/Gastric inhibitory peptide (GIP).
  • Kidney: Hormones: Renin, Erythropoietin, Calcitriol (active vitamin D3).
Heart
  • Hormone: Atrial Natriuretic Factor (ANF).
  • Increases sodium excretion and reduces blood pressure.
  • Secreted when blood pressure rises, causing blood vessel dilation.

Hormone Therapy/HT: Use in medical treatment for conditions like pregnancy, menopause, osteoporosis, growth hormone deficiency, insulin resistance, and cancer.