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Controlling and Co-ordinating System


Classification and functions of epithelial tissue

Q.State three important features of epithelial tissue.

All epithelial tissues except glandular ones share certain common characteristics, as follows—

i)   Relatively cells are regular in shape and closely packed in continuous sheets, with little or no extracellular matrix.

ii) Tight fitting epithelial cells are held in place by ell cell junctional complexes of plasma membrane (tight junction, spot desmosome, gap junction etc).

iii)  Most epithelial cells are anchored to the underlying connective tissue by a basement membrane (composed of basal lamina, reticular lamina).

Classification and functions of connective tissue

Q.Give examples of 5 cell types of connective tissue.

Fibroblasts, plasma cell, mast cell, macrophage and leukocytes.

Q.What is collagen?

The collagens constitute a family of protein selected during evolution for the execution of several (mainlystructure) functions. During the process of evolution of multicellular organisms, a family of structuralproteins that was modified by environmental influences and the functional requirements of the animal organism developed to acquire varying degree of rigidity, elasticity and strength. These proteins are known collectively as collagen and the primary examples among its various types are present in the skin, bone, cartilage, smooth muscle and basal lamina.

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SEM of Collagen connective tissue fibres

(Ref: Photo Library Ltd,2019)

Classification and functions of muscular tissue
Classification and functions of nervous tissue
Structure and types of bones

Q.Distinguish between osteoblast and osteoclast.

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Structure and types cartilages
Structure of neuron
Resting membrane potential
Origin of action potential and its propagation across the myelinated and non-myelinated nerve fibres

Q.What do you mean by depolarization stage?

This is the stage when action potential develops in response to stimulation. Stimulation at some point of normal resting membrane leads to opening of Na+-ions through Na+ gated channels that reaches its peak very quickly (0.1ms). Normal polarized state of —90 mV is lost. With the potential rising rapidly in the positive direction. Reversal of ionic currents with positivity (+) inside and negativity (-) outside.

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(Ref: Pearson Education, Inc. Benjamin Cummings)

Types of synapse
Synaptic transmission and Neuromuscular junction
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Q.Define neuromuscular junction.

The axon terminals of motor neurons make a specialized region of contact with the skeletal muscle fiber membrane and this region is called neuromuscular junction. Through neuromuscular transmission a nerve action potential is transformed to a muscle action potential. It is considered as a large peripheral synapse as its mechanism of operation is similar to a synapse. The neurotransmitter in these locations may be acetylcholine (ACh) or norepinephrine (NE).

Histology of different types of muscle
Ultra-structure of skeletal muscle
Molecular and chemical basis of muscle contraction

Q.State the functional importance of titin and nebulin.

Muscle fibers contain specialized proteins in addition to actin and myosin. titin and nebulin are structural proteins that help align the contractile proteins actin and myosin. Titin has elastic properties and a single molecule spans the distance between Z disc and the M line. Titin confers the ability to spring back after the muscle fiber is stretched. Whereas nebulin is inelastic, runs the length of a thin filament and stabilizes it.

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Characteristics of muscle fibre
Histology of mammalian testis and ovary

Q.Briefly state the histological arrangement of sertoli cells.

The Sertoli cells are elongated pyramidal cells that are partially envelop cells of the spermatogenic lineage. The bases of the Sertoli cells adhere to the basal lamina and their apical ends frequently extend into the lumen of the seminiferous tubule. Light microscopic study revealed that the outlines of Sertoli cells appear poorly defined because of the numerous lateral processes that surround spermatogenic cells. Studies with the electron microscope reveal that these cells contain abundant smooth endoplasmic reticulum, some high RER, a well developed Golgi complex and numerous mitochondria and lysosomes. Adjacent Sertoli cells are bound together by occluding junctions at the basolateral part of the cell, forming a blood-testis barrier.

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Physiology of mammalian reproduction
Menstrual cycle
Estrous cycle
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Q.Define estrous cycle.

The estrous cycle or estrous cycle is the recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases or by pregnancies. Typically, estrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation. The changes in the histology of the female reproductive organs in vertebrates occur regularly in the estrous cycle. Cyclical changes in the secretion of hormones from pituitary, gonad, uterus, etc. sponsor such changes. From the histological changes in the vaginal epithelium, different stages of the estrous cycle are identified. The vaginal epithelium is torn down and rebuilt cyclically, fluctuating between the stratified epithelium and low cuboidal epithelium.

Histology and function:

Q.Compare the histological organization of adrenal cortex and medulla.

Histological organization of adrenal cortex:

Composed of large, cholesterol rich cells arranged in 3 morphologically distinct zones. They are—

(a)Zona glomerulosa:

i)The outer zone that lies under a fibrous capsule. It comprises about 5-10% of cortex. Cells are comprises about 5-10% of cortex.

ii)Cless are closely packed and form small, ill defined clumps, in humans but in other species cells are arranged in a continuous thin layer (For further information follow contact zone)

(b)Zona fasciculata:

i)The middle cortical zone that forms the bulk of the gland (~75% of the volume of adrenal cortex).

ii)Cells are larger than those in Zona glomerulosa.

iii)Cells are arranged in long cords disposed radially with respect to medulla (For further information follow contact zone).

(c)Zona reticularis:

The dippest layer of adrenal cortex, comprises anastomosing network of short cords of cells with interdigit capillaries (For further information follow contact zone).

Histological organization of medulla:

i)Composed of chromaffin cells, which show brown colouration when exposed to aqueous solution of K2Cr2O7.

ii)Cells arranged in anastomosing epithelioid cords, separated by vascular spaces— specially capillaries (For further information follow contact zone).

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Function of pituitary
Classification of hormones
Mechanism of Hormone action
Signal transduction pathways
Steroidal hormones

Q.State the basic mechanism of steroid hormone transport.

When steroid hormone released into the circulation, the gonadal steroids bind to plasma proteins. Estradiol binds avidly to a transport globulin called sex horomone binding globulin (SHBG) and binds with the less affinity to albumin. Progesterone binds strongly to cortico-steroid binding globulin (CBG) and weakly to albumin. The concentration of these binding proteins is increased by estrogen and thyroxine and decreased by androgens and progestins (Progestin is a form of progesterone, a hormone that plays a role in the menstrual cycle and pregnancy. Progestin is used in combination with another hormone called estrogen in combined hormonal birth control pills, the vaginal ring, and the skin patch).

SHBG is synthesized in the liver and because its synthesis is stimulated by estrogens and inhibited by androgen, levels are twice as high in women as in men. The proportions of free and bound estradiol do not vary significantly during the menstrual cycle.

Non- steroidal hormones
Hypothalamus (neuroendocrine gland)
Nuclei involved in neuroendocrine control of anterior pituitary
Placental hormones

Q.Mention two protein hormone of placenta along with their functional significance.

Several protein and peptide hormones are synthesized in placentae of various species. They have effects on the mother's endocrine system, fetal metabolism and preparation of the mother for postpartum support of her offspring.

(1)Chorionic gonadotropins: These hormones have the effect of stimulating the gonads, similar to the pituitary gonadotropins. The only species known to produce a placental gonadotropin are primates and equids.

The human hormone is called human chorionic gonadotropin or simply hCG. This hormone is produced by fetal trophoblast cells. It binds to the luteinizing hormone receptor on cells of the corpus luteum, which prevents luteal regression. Thus, hCG serves as the signal for maternal recognition of pregnancy. The first hormone you produced was hCG!

(2)Placental lactogens: These hormones are molecular relatives of prolactin and growth hormone. These hormones have been identified in primates, ruminants and rodents, but not in other species.

They are thought to modulate fetal and maternal metabolism, perhaps mobilizing energy substrates for fetal use. In some species they have been shown to stimulate function of the corpus luteum, and to participate in development of the mammary gland prior to parturition.

Honours / Core Course (CC)

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