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.

 

Hormones

• 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.

 

Pancreas 

• 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.

 

Testis

• 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.

 

Ovary 

• 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.
  
  

 

Feedback Mechanism of Hormone Action

 

Negative Feedback Mechanism

• The body has mechanisms to maintain a normal state.
• Whenever there is a change in the normal state, the messages are sent to increase secretions if there is a fall below normal or to decrease secretions if there is a rise above normal to restore the normal body state. Such a mechanism is called Negative Feedback Mechanism.
  
  

 

 

• Example: Blood sugar level
  The increase in blood sugar level stimulates the secretion of insulin so that the sugar level is maintained. If there is a fall in the blood sugar level below normal, then it stimulates the secretion of glucagon. Glucagon stimulates the breakdown of glycogen to glucose, and thus, the normal sugar level is maintained.

 

Positive Feedback Mechanism

• It is very rare.
• Example: Uterine contractions during childbirth
• In the normal state, the uterine muscles are relaxed. One contraction of these muscles stimulates the secretion of oxytocin which further increases the contraction of uterine muscles.

 

Nervous Coordination in Animals

 

• The nervous co-ordination is brought about by the nervous system.
• Functions of the Nervous System:

• Keeps us informed about the outside world through sensory organs.
• Controls and harmonises all voluntary muscular activities, e.g. running and writing.
• Enables us to remember, think and reason.
• Regulates involuntary activities such as breathing and beating of the heart.

 

Nervous System in Hydra

• Hydra belongs to phylum Cnidaria of the group invertebrate. 
• The nervous system in Hydra is merely a network of nerve cells joined to one another and spread throughout the body between the two gem layers, outer epidermis and inner gastrodermis. This network is called nerve net.
  
  

 

• The nerve cells morphologically are of two types:

1. Sensory neurons
2. Ganglion neurons

• The contractions and the extension of the tentacles and the body, the different types of locomotory movements like gliding, floating, walking, looping, and somersaulting are all under the control of the nervous system of Hydra.
• When the body of hydra receives certain stimulus at a particular region from the environment, the nerve cells present at the region send impulses in all directions through the network of nerve cells spread throughout the body. 
• In this way, nerve network coordinates responses to different stimuli in Hydra without the existence of central control region i.e. brain.

 

Nervous System in Grasshopper

• In insects such as grasshopper, the nervous system consist of a brain, ganglia and nerve cord. 
• A mass of nerve cells is called ganglion. The nerve cord runs along the entire length of the body. 
• At interval, it shows the presence of ganglia. Small nerves are given out from each ganglion. 
• Near the anterior end of the insect body, a large bilobed ganglion, called the brain, is present. 
• Thus the nervous system of grasshopper consist of a brain, a long nerve cord, the ganglia and nerves spreading form the nerve cord.
  
  

 

Nervous System in Humans

• The nervous system of human beings is composed of neurons. These are surrounded by a connective tissue called neuroglia.
• Neuron is the structural and functional unit of nervous system. It is the longest cell found in the body.

 

Structure of the Neuron

 

 

 

The three main parts of the neuron are as follows:

• Cell Body: It has a well-defined nucleus and granular cytoplasm.
• Dendrites: They are the branched cytoplasmic projections of the cell body.
• Axon: 

• It is a long process of the cell body.
• The axon is covered by a myelin sheath.
• The myelin sheath shows gaps throughout its length known as Nodes of Ranvier.

 

Some Basic Terms

 

Nervous Pathways in Reflexes

 

A reflex action must be quick to give quick response. Therefore, the pathway for receiving and sending information must be short.

 

A reflex arc can be represented as follows:

Stimulus → receptor in the sense organs → afferent (sensory) nerve fibre → CNS (spinal cord/brain) → efferent (motor) nerve fibre → muscle/gland → Response