Animal Physiology

• Major endocrine glands/organs


  • Pituitary Gland
  • Thyroid glands
  • Parathyroid glands
  • Adrenal glands
  • Pancreas

  
• MSH


  Melanocyte-stimulating hormone
• ADH


  Antidiuretic hormone
• Growth Hormone


  • Stimulates tissue growth
  • Facilitates protein synthesis and slows down amino acid catabolism
  • Promotes transfer of blood amino acids into muscle cells resulting in a positive nitrogen balance
• ACTH


  • ACTH secretion is regulated by corticotropin releasing factor (CRF) and glucocorticoids level in the plasma
  • Stimulates the release of cortical hormones: cortisol, corticosterone, aldosterone, etc.

  
• Thyroid Stimulating Hormone (TSH)


  • Secretion is controlled by a thyroid releasing factor (TRF) and maintained by circulating TSH and thyroid hormones

  
• Follicle Stimulating Hormone (FSH)


  • Females: Leads to growth and maturation of graafian follicles with estrogen production
  • Males: Induces development of the germinal epithelium of the seminiferous tubules

  
• Luteinizing Hormone (LH)


  • Females: Promotes formation of corpus luteum which secretes progesterone
  • Males: Stimulates the interstitial cells of the testis to produce testosterone

  
• Prolactin


  • Responsible for maintaining corpus luteum of pregnancy
  • Responsible for the release of milk in female mammary glands

  
• Melanocyte-Stimulating Hormone (MSH)


  • Fish, amphibians and reptiles: Darkening of the skin by dispersing melanocytes or pigment cells
  • Humans: Darkening of the skin; Regulation is controlled by the sunlight
  • Lack of skin pigmentation is due to its absence
  • Experiments have proved that hypothalamus controls the secretion of MSH
• Oxytocin


  • Stimulating effect on the musculature of the uterus and promotes labour
  • Used to induce child birth
  • Stimulates secretion of milk from the breasts and the stimulus is obtained from the suckling of the baby

  
• Thyroid hormones


  • Thyroxine (tetraiodothyronine): Principal hormone
  • 3,5,3'—triiodothyronine: 5x more powerful
  • 3,3',5—triiodothyronine
  • 3,3'—diiodothyronine
  • Calcitonin

  
• Adrenal cortex


  • Hormonal secretion is regulated by CRF from the hypothalamus and ACTH from the anterior pituitary
  • Glucocorticoids (metabolocorticoids): Affect the carbohydrate and protein metabolism, such as cortisone, cortisol and hydrocortisone
  • Mineralocorticoids (aldosterone): Sodium absorption and potassium excretion
  • Androgens: Sex and anabolic hormones

  
• Adrenal medulla


  • Secretes catecholamines: Epinephrine (adrenaline) and nor-epinephrine (noradrenaline)
  • Innervated by neurons of sympathetic nature which when activated stimulate the section of these hormones
  • Medullary tissue is also stimulated by different centers in hypothalamus

  
• Insulin and glucagon


  Hormones produced by the pancreas
• Hormonal Regulation in Invertebrates - Annelida


  • Cerebral ganglia have neurosecretory cells which undergo seasonal secretory cycles related to growth and reproduction
  • Brain cells release a hormone (unknown chemical nature)
  • Brain hormone may inhibit the development of germ cells, or it may stimulate sexual characters

  
• Hormonal Regulation in Invertebrates - Mollusca


  • Neurosecretions influence the reproduction in molluscs
  • Production of eggs or sperms is controlled by neurosecretory cells
  • Optic glands regulate the onset of sexual maturity in either sex
  • Optic glands are believed to secrete a gonad-regulating hormone under nervous control of brain

  
• Hormonal Regulation in Invertebrates - Insects

  • Possess a highly organized endocrine system
  • Processes of growth, development and metamorphosis in insects are controlled by hormonal mechanisms
  • Neurosecretory cells present in the brain comprising pars intercerebralis, corpora cardiaca and sub-oesophageal ganglia
  • Other endocrine glands include prothoracic glands and corpora allata
  • The neural glands and the endocrine glands are intimately interrelated for coordinating secretory activities almost like that of vertebrates

  
• Diapause


  • Resting stage represents a physiological mechanism for survival during adverse conditions
  • Can occur during embryonic stage, larval stage, or in pupa
  • During this stage, the metabolic rate is extremely low with a complete or partial cessation of growth
• Hormonal Regulation in Invertebrates - Crustacea

  • Eye stalk cells secrete a gonad-inhibiting hormone and its absence initiates yolk production
  • The hormone from the sinus gland also inhibits vitellogenesis and moulting in egg-bearing females
  • The pericardial glands secrete a hormone that maintains the heart beats
  • Moult inhibiting hormone (MIH)
  • Mandibular Organ Inhibiting factor (MOIH)

  
• Levels of Reproduction


  • Molecular
  • Cellular
  • Organismal
• Patterns of Reproduction


  • Asexual Reproduction
  • Sexual Reproduction
• Testes


  Male gonads where the sperms are produced
• Spermatogenesis


  1. Differentiation and maturation of spermatogonia in the testes

  2. Primary spermatocytes (diploid chromosomes) undergo two meiotic divisions

  3. Resulting cells are called spermatids, each of which transforms itself into a sperm or spermatozoa (haploid chromosomes)

  4. Each primary spermatocyte eventually gives rise to four spermatozoa
• Ovaries


  Female gonads where the oocytes are produced
• Oogenesis


  1. Inside the ovary the primary oocytes undergo two meiotic divisions

  2. As a result, a secondary oocyte and a first polar body are produced

  3. Secondary oocyte and the first polar body undergo reduction division

  4. Secondary oocyte again divides to give rise to an ovum and another polar body
• Gonadal Hormones


  • Testicular Hormones
  • Ovarian Hormones

  
• Testicular Hormones - Androgens

  • Male hormones secreted by the interstitial tissues of the testis
  • Testosterone is the principal male hormone synthesized by the interstitial cells (Leydig cells) of the testis
  • Helps in muscular and skeletal growth spurt at puberty

  
• Ovarian Hormones - Estrogens

  • Synthesized in the ovary, adrenal cortex, placenta and Leydig cells
  • Induce estrous cycle and help in maintenance of secondary sex characters and the accessory sex organs

  
• Ovarian Hormones - Progesterone

  • Luteal hormone synthesized by corpus luteum, adrenal cortex, placenta and the testis
  • Pregnancy hormone which acts on genital tissues and induces proper functioning of breast
• Ovarian Hormones - Relaxin


  • Produced by the corpus luteum and small amounts in the placenta
  • Causes softening of epiphysis and facilitates delivery

  
• Estrous cycle


  • Period of heat when the ovaries are considerably enlarged and deep red in color due to maximal development of ovarian follicles
  • Includes the ripening of a follicle, rupture of the follicle and release of the ovum, and behaviour of the organism at the time of ovulation for achieving successful fertilization
  • Proestrus – Estrus – Metestrus - Diestrus
• Menstrual cycle


  • Menstruation occurs only in primates
  • Characterized by sloughing of the uterine endometrium completely
• Gonadotropic or follicular hormones


  Induce estrous cycle and help in maintenance of secondary sex characters and the accessory sex organs

  
• Progesterone


  A luteal hormone synthesized by corpus luteum, adrenal cortex, placenta and the testis. It is a pregnancy hormone which acts on genital tissues and induces proper functioning of breast

  
• Relaxin


  Produced by the corpus luteum and small amounts in the placenta which causes softening of epiphysis and facilitates delivery
• Estrous cycle


  • Period of heat when the ovaries are considerably enlarged and deep red in color due to maximal development of ovarian follicles
  • Includes the ripening of a follicle, rupture of the follicle and release of the ovum, and behaviour of the organism at the time of ovulation for achieving successful fertilization
  • Proestrus - Estrus - Metestrus - Diestrus
• Menstrual cycle


  • Menstruation occurs only in primates
  • Characterized by sloughing of the uterine endometrium completely accompanied by vaginal bleeding
  • In contrast to non-primates having short period of heats, the primates permit copulation throughout the whole cycle
  • Ovulation generally occurs midway between two menstruating cycles or 12 to 15 days following the beginning of menstruation
  • Individual variations in the cycle are also found where the normal cycle is prolonged up to 33 days
  • Proliferative - Ovulatory - Progestational - Menstrual
• Ovulation


  • Involves the rupture of ripe follicles and release of the ovum
  • Spontaneous ovulators: ovulation occurs shortly before or after the end of heat
  • Induced ovulators: ovulation is induced by certain acts like genital stimulation, copulation, etc.
  • Requires a sudden increase in the secretion of luteinizing hormone (LH) over a period of a few minutes
  • Fertilized or unfertilized eggs are propelled through the oviduct aided by peristaltic waves set up in the oviduct walls
  • Progesterone accelerates progression of the ovum through the oviduct, whereas estrogen arrests the egg movement

  
• Sperm transport in the female genital tract

  • During coitus, the sperms are deposited either in the vagina or in the uterus
  • Fertilization occurs in the oviduct
  • Sperms are transported rapidly to the oviduct by muscular activity of the uterus, oviduct and the ciliary activity of the epithelial lining of the oviduct
  • Oxytocin is essential for the rapid transport of sperms from the cervix to the oviduct
  • Capacitation: spermatozoa do not fertilize ova unless they have undergone a period of incubation in the female tract
  • Capacitation of sperms is influenced by hormonal conditions and exposure to cervical, uterine or tubal secretions before they acquire the ability to fertilize the ova
  • Due to capacitation, spermatozoa lose their microsomal cap allowing release of subtances necessary for penetration of egg
  • Capacitated sperms show a higher metabolic activity