Endocrine Glands, Integuments and Sense Organs | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Endocrine Glands Simplified

1. Definition:

   • Endocrine glands are special glands in our body that release hormones directly into the bloodstream.
   • They can be individual organs (like the pituitary, adrenal, and thyroid) or parts of other organs (like islets in the pancreas).

2. Characteristics:

   • They are ductless, meaning they release hormones directly into the blood.
   • These glands can be standalone organs or part of other organs.
   • They are often well-vascularized and may be encapsulated.

3. Thyroid Gland:

   • Composed of thyroid follicles filled with a gel-like substance called colloid.
   • Follicular lining cells and parafollicular cells (C cells) are involved.
   • Secretes hormones T4 (thyroxine) and T3 (triiodothyronine), as well as calcitonin.

4. Parathyroid Gland:

   • Found in the neck, usually as four small glands.
   • Chief cells and oxyphil cells produce parathormone, which regulates calcium levels in the blood.

5. Adrenal Gland:

   • Divisible into cortex and medulla.
   • Cortex produces mineralocorticoids, glucocorticoids, and sex hormones.
   • Medulla produces adrenaline (epinephrine) and noradrenaline (norepinephrine), affecting blood pressure and sugar levels.

6. Pituitary Gland:

   • Divided into anterior and posterior lobes.
   • Anterior lobe secretes various hormones like growth hormone, prolactin, and thyroid stimulating hormone.
   • Posterior lobe releases oxytocin and antidiuretic hormone.
   • Hypothalamus regulates pituitary gland function.

7. Pineal Gland:

   • Produces melatonin and serotonin, affecting sleep-wake cycles.
   • Covered by connective tissue, with astrocytes and pinealocytes as main components.

8. Pancreas:

   • Islets in the pancreas have alpha cells (secreting glucagon) and beta cells (secreting insulin).
   • Plays a crucial role in regulating blood sugar levels.

9. Reproductive Glands (Ovaries and Testes):

   • Ovaries produce estrogen and progesterone.
   • Testes produce androgens.
   • Both affect reproductive and somatic structures and functions.

10. Placenta:

    • Secretes hormones like estrogen, progesterone, placental gonadotropins, and prostaglandins during pregnancy.

This system of glands helps regulate various bodily functions by releasing hormones that act as messengers, influencing growth, metabolism, and reproductive processes.

Integuments

Understanding the Skin Simplified:

1. Basic Functions:

   • The skin acts as a protective barrier for the body.
   • It helps regulate body temperature and excretes waste.
   • Contains various structures like hair follicles, glands, and nails.

2. Composition:

   • Consists of the epidermis (outer layer) and dermis (inner layer).
   • Structures like hair, nails, and horns are derived from the skin.

3. Epidermis Layers:

   • Epidermis is a layered structure with a deep layer (stratum germinatium) and a superficial layer.
   • Layers include stratum cylindricum, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
   • Cells in the outer layer (stratum corneum) are made of keratin, with no nucleus.

4. Dermis Composition:

   • Dermis is below the epidermis and made of irregularly arranged connective tissues.
   • It has fibroblasts, histiocytes, and two layers – subepithelial papillary layer and deeper reticular layer.

5. Hair Structure:

   • Hairs are flexible threads developed from the skin's outer layer (epidermis).
   • Each hair has a shaft and a root, with a bulb-like expansion called the hair bulb at the root.
   • The hair follicle surrounds the root, consisting of both epidermal and dermal parts.

6. Gland Types:

   • Sebaceous glands, associated with hair follicles, are holocrine (release entire cells).
   • Sweat glands come in two types – merocrine and apocrine.

7. Skin Thickness:

   • Skin thickness varies across the body.
   • Palms, soles, and the underside of digits have thicker skin with distinct layers.

8. Skin Color:

   • Skin color is mainly due to melanin pigment in specialized cells called melanocytes.
   • Melanin gives color to the skin, hair, and eyes.

Sense Organs

Understanding Sensory Systems Simplified

1. General Overview:

   • The body's response to internal and external stimuli depends on sensory receptors distributed throughout the body.
   • Sensory receptors can be classified into somatic and special sensory systems, the latter further divided into general and visceral components.

2. Special Sensory System:

   • Includes special somatic afferent (SSA) system (eye and ear) and special visceral afferent (SVA) system (taste and smell).

3. Eye:

   • The eyeball consists of the cornea, pupil, iris, lens, ciliary body, retina, and muscles.
   • Photosensitive cells (rods and cones) in the retina convert light into usable information.
   • The eye has three layers: fibrous (sclera and cornea), vascular (choroid, ciliary body, and iris), and nervous (retina).

4. Nictitating Membrane (Third Eyelid):

   • A fold of conjunctiva with cartilage in some animals.
   • Secretions vary among animals, with different gland types like seromucoid and mucoid.

5. Ear:

   • Responsible for hearing and balance.
   • Components include auricle, auditory meatus, tympanic membrane, ossicles, cochlea, and the organ of Corti.
   • Vestibular portion includes semicircular canals, utriculus, and saccules.

6. Taste Buds:

   • Receptors for taste sensations found in tongue papillae.
   • Taste buds are ovoid structures with tiny taste hairs.
   • Different taste sensitivities (sweet, salty, sour, bitter) are distributed across the tongue.

7. Olfactory Cells:

   • Specialized area for smell located in the nose.
   • Thick lamina epithelialis with sustentacular cells, basal cells, and olfactory cells.
   • Olfactory cells are modified neurons with olfactory vesicles and hairs.

8. Overall Function:

   • Sensory systems help the body respond to its surroundings.
   • Eyes process visual information, ears handle auditory and balance functions, taste buds perceive flavors, and olfactory cells detect smells.