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Coordination in Animals

Coordination in Animals Synopsis



Control and Coordination 

  • Control is the power of restraining and regulation by which something can be started, slowed down or stopped. 
  • Co-ordination is the working together of various agents of the body of an organism in a proper manner to produce an appropriate reaction to a stimulus.
  • The mechanism of maintaining internal steady state is called homeostasis

Chemical Coordinationin Animals
Coordination in animals is brought about by the secretions of endocrine glands.
In man and other higher vertebrates, there are three types of glands.
  1. Exocrine Glands: These are the glands with ducts. They discharge their secretions on the body surface or in body cavities.
  2. Endocrine Glands: These are ductless glands. Their secretions are directly poured into the blood.
  3. Heterocrine Glands: They are mixed type of glands. They have their exocrine as well as endocrine part.
  • A hormone, also called a chemical messenger, is a secretion from some glandular part of the body which is poured into the blood and which acts on the target organs or cells of the same individual.
  • Categories of hormones:
    • Steroid hormones: oestrogen, progesterone
    • Modified amino acids: thyroxine, epinephrine
    • Polypeptides: insulin, glucagon
    • Proteins: somatotropic hormone, follicle-stimulating hormone
    • Glycoproteins: luteinising hormone, thyroid-stimulating hormone
General Properties of Hormones
  • Hormones are produced in very small quantities.
  • Hormones produced in one species usually show similar influence in other species.
  • They are not stored in the body. Excess quantities in the blood are excreted.
  • Excess secretion or deficiency may lead to serious disorders.
Functions of Hormones
  • Hormones control the rate of basal metabolism.
  • They control growth, development and differentiation of the body tissue of organisms
  • They influence the mental ability.
  • They regulate adaptations to external factors.
The endocrine system is consists of following glands:

The Hypothalamus  
  • The hypothalamus is a part of the brain which consists of several masses of grey matter called hypothalamic nuclei.
  • Neurons of hypothalamic nuclei synthesise chemicals which are secreted into the blood.
  • The hormones secreted by the hypothalamus regulate the synthesis and secretion of pituitary hormones. 
  • The hormones secreted by the posterior lobe of the pituitary are synthesised by neurons in the hypothalamus and stored in their axon ends in the posterior lobe for release.

Hormones of the Hypothalamus
The Pituitary Gland
  • The pituitary gland is located in sella tursica and it is attached to the hypothalamus by a stalk.
  • The gland is divided into three lobes 
    1. Anterior lobe (adenohypophysis)
    2. Intermediate lobe 
    3. Posterior lobe (neurohypophysis)

Secretions of Anterior Pituitary

1. Growth Hormone
  • It is essential for the normal growth. 
  • It is also known as somatotropin.
  • Its deficiency causes disorders such as dwarfism and gigantism.
  • Its over secretion of growth hormone results in acromegaly.
2. Thyroid Stimulating Hormone (TSH)
  • TSH controls the synthesis and secretion of thyroid hormones from the thyroid gland.
3. Gonadotropins
  • Luteinising hormone (LH) and follicle stimulating hormones (FSH) are the gonadotropins.
  • In female, LH stimulates the ovulation, formation of the corpus luteum and secretion of progesterone.
  • In male, LH stimulates the secretion of androgens in testes. Androgens stimulate the secretion of testosterone.
  • In females, FSH stimulates the growth and development of ovarian follicles.
  • In males, FSH promotes spermatogenesis.
4. Adrenocorticotropic Hormone (ACTH)
  • ACTH regulates the synthesis and secretion of glucocorticoids from the adrenal cortex.
Secretions of Intermediate Lobe

1. Melanocyte Stimulating Hormone (MSH) stimulates melanocyte present in the skin and hence controls the pigmentation.
Secretions of Posterior Pituitary

1. Oxytocin
  • It stimulates the contraction of uterine muscles during the child birth.
  • It also stimulates ejection of milk from the mammary glands post-delivery.
2. Vasopressin/Anti-diuretic Hormone
  • It stimulates the resorption of water and electrolytes by DCT in the kidneys.
  • Hence, it helps in reducing water loss through urine.
The Pineal Gland 
  • The pineal gland arises from the roof of the third ventricle which lies between the two cerebral hemispheres attached to a stalk-like structure.
  • It is located on the dorsal side of the forebrain.
  • It secretes the hormone melatonin which regulates the 24-hour diurnal rhythm of the body (e.g. the sleep–wake cycle) and body temperature.
Parathyroid Glands
  • There are four small glands present at the back side of the thyroid gland.
  • The hormone secreted by the parathyroid glands is parathormone or parathyroid hormone (PTH).
  • Parathormone controls metabolism and maintains blood calcium level.
  • Hyposecretion of parathormone causes tetany and its hypersectrion causes demineralisation of bones.

Thymus Glands  
  • Thymus gland is located on the dorsal side of the heart and aorta.
  • It secretes two hormones — thymopoietin and thymosin.
  • Thymosin controls the maturation and distribution of lymphocytes.
  • It stimulates the production of antibodies.
Adrenal Gland 
  • Adrenal glands, also called suprarenals, are a pair of yellowish, pyramid-shaped, small glands present on the upper side of the kidneys.

  • Each adrenal gland consists of the outer adrenal cortex and the inner adrenal medulla.

Secretions of Adrenal Cortex
1. Mineralocorticoids (aldosterone)
  • They regulate mineral metabolism.
  • They stimulate the kidneys to retain sodium and to excrete potassium.
2. Glucocorticoids
  • They regulate the carbohydrate, fat and protein metabolism.
  • Certain cortical hormones function as sex hormones as they regulate the development of reproductive organs.
    Hyposecretion of adrenal cortex results in Addison’s disease and its hyper secretion causes Cushing syndrome.
Secretions of Adrenal Medulla
Adrenaline and Noradrenaline
  • These hormones are also called as epinephrine (adrenaline) and norepinephrine (noradrenaline).
  • These are the hormones of fight or flight response.
  • The hormones increase the alertness, pupilary dilation, sweating, increase in heart beat, increase in the rate of respiration during fight or flight response.
  • It is a heterocrine gland. Some part of the pancreas is exocrine and some part is endocrine.
  • The exocrine part pours its secretion—pancreatic juice—into the duodenum through the pancreatic duct.
  • The endocrine part is made of a special group of cells known as the islets of Langerhans.
  • Three kinds of cells found in the islets of Langerhans. α – cells secrete glucagon, β – cells secrete insulin and δ – cells secrete somatostatin.

  • Glucagon raises the blood glucose (hyperglycemia) level by promoting the glycogenolysis i.e. breakdown of glycogen into glucose in the liver. It also accelerates the gluconeogenesis i.e. it reduces the cellular uptake of glucose which results in increase in blood glucose level.
  • Insulin lowers the blood glucose level (hypoglycemia) by increasing the cellular uptake of glucose. It stimulates the glycogensis i.e. the conversion of glucose into glycogen in the liver.
  • Deficiency of insulin leads to the prolonged hyperglycemia resulting into diabetes mellitus.
  • A pair of testes is present in the scrotal sac.
  • Testes are both exocrine and endocrine.
  • The endocrine part of each testis is formed of a group of cells called interstitial cells or Leydig cells.
Hormones Secreted By Testis
1. Testosterone 
  • It helps in maturation of sperms. 
  • It stimulates the growth and development of the male reproductive system.
  • It stimulates the development of secondary sexual characters.
  • The failure of testosterone secretion causes.
2. Androsterone
  • It is an androgen which affects the masculinisation of the foetus and child, and maintains or creates masculine traits in adults.
  • It stimulates the process of spermatogenesis.
  • Ovaries are female gonads that are both exocrine and endocrine in function. 
Hormones Secreted By Ovaries
1. Oestrogen
  • It promotes the development of ovarian follicles.
  • It stimulates the growth and activities of female secondary sex organs.
  • It regulates the female sexual behavior.
2. Progesterone
  • It promotes the development of placenta.
  • It promotes the development of the mammary glands during pregnancy and inhibits the contraction of the uterus.