Hormonal Coordination in Mammals.

The mechanism of controlling the release of hormones by the glands is as follows:

1. Presence of specific metabolite in the blood. For example, presence of excess glucose in the blood causes the release of insulin.
2. Presence of another hormone in the blood. Many of the hormones released by the anterior pituitary cause the release of other hormones.
3. Stimulation by neurons from autonomic nervous system. For example, adrenaline and noradrenaline are released by the adrenal gland following the arrival of impulses in the condition of anxiety, stress and danger.

Feedback mechanism is a self regulating mechanism in the body which tends to restore the physiological equilibrium or stability of the body or increase in the instability of the body.

1. Positive Feedback: This is a type of feedback that tends to increase the effect of the disturbance. Positive feedback responses are rare in biological systems because they increase instability of the body.

2. Negative Feedback: This brings the body back to its normal physiological states. Thus the negative feedback mechanisms are important in the biological systems.

   Examples of biological negative feedback mechanisms include the control of heartbeat, blood pressure, body temperature and hormone levels i.e. secretion of insulin.

N.B:

• TRF: Thyroid Releasing Factor
• TSH: Thyroid Stimulating Hormone

Note:

• Example of Positive Feedback: During labor, the hormone oxytocin stimulates muscular contraction of the uterus, which in turn stimulates the release of more oxytocin.

Interaction between hormonal and nervous systems

The two coordinating systems, i.e., the hormonal and nervous systems, sometimes depend on one another. For instance, the release of hormones can depend on responses reaching the gland through nerve cells.

Example:

• Adrenaline and Noradrenaline are released by the adrenal gland in response to impulses during conditions of danger, anxiety, and stress.
• This demonstrates how the hormonal and nervous systems depend on each other for coordinating body functions.

Nervous and hormonal control of secretion

In mammals, the production of digestive secretions is regulated by both the nervous and hormonal systems.

1. Nervous Stimulation:

   • Occurs before food reaches the mouth.
   • The sight, smell, or thought of food triggers the salivary glands to produce saliva.

2. Saliva Secretion:

   • As explained, the sight, smell, and thought of food can trigger saliva secretion.
   • The presence of food on the tongue further stimulates saliva production.

Note: There are three important hormones secreted in the stomach and small intestinal region:

1. Gastrin
2. Secretin
3. Cholecystokinin (CCK)/Pancreozymin

Gastrin

1. Source: Released by the stomach walls in response to the presence of food.

2. Mechanism:

   • It enters the bloodstream and stimulates the production of gastric juice from gastric glands.
   • Gastric juice production continues for about 40 minutes.

Note:

1. The digestion of fats takes longer and requires less acidic conditions.
2. The presence of fats in the stomach triggers the production of a hormone called progesterone, which inhibits further secretion of acid by the oxyntic cells of the stomach.

Secretin

1. Source: Produced by the small intestinal wall cells.

2. Target Organs and Effects:

   • Stomach: Inhibits gastric juice secretion by blocking gastrin release.
   • Liver: Stimulates the production of bile, including NaHCO₃ (sodium bicarbonate) for neutralizing acidic chyme.
   • Pancreas: Stimulates the secretion of alkaline salts like NaHCO₃.

Cholecystokinin (CCK) / Pancreozymin

1. Source: Produced by the small intestinal wall cells.

2. Target Organs and Effects:

   • Stomach: Inhibits stomach emptying.
   • Pancreas: Stimulates the secretion of pancreatic juice into the duodenum.
   • Liver: Causes contraction of the gall bladder, leading to the release of bile through the bile duct.

Epithelial and glandular tissues in relation to their digestive roles

Epithelial Tissue:

1. A type of tissue that covers the external and internal surfaces of the body, such as the lining of the alimentary canal.
2. Functions:
   • Diffusion and Transport: Allows exchange of substances.
   • Secretion: Produces substances like mucus.
   • Protection: Shields underlying tissues.

Example: columnar epithelial tissue

1. Structure:

   • Consists of elongated cells with a narrow shape, providing more cytoplasm per unit area.
   • Each cell has a nucleus at the basal end and may contain goblet cells.
   • The free surface has a striated or brush border of microvilli.

2. Location:

   • Found in the stomach, small intestine, kidney ducts, and thyroid gland.

3. Functions:

   • Mucus secretion: Goblet cells in the stomach protect the lining from acidic contents and digestion by enzymes.
   • Protection in the Small Intestine: Mucus prevents self-digestion and lubricates food passage.
   • Increased Absorption: Microvilli increase surface area for nutrient absorption in the ileum.

Comparison: hormonal and nervous systems

There are ductless glands that secrete hormones directly into the blood stream. Such glands include:

Location of hormones in improving human life and animal husbandry

Synthetic hormones have significantly improved both human life and animal husbandry by enhancing various biological processes.

1. In animal husbandry:

1. Growth Hormones:
   • Used to promote rapid growth in animals such as chickens and cows.
2. Reproductive Hormones:
   • Enhance egg production in poultry.
3. Lactation Hormones:
   • Prolactin and Oxytocin are administered to cows and goats to increase milk production.

2. In humans:

1. Synthetic Oxytocin:
   • Used to induce labor during childbirth.
2. Contraceptive Hormones:
   • Synthetic sex hormones (e.g., progesterone) are used in contraceptive pills to prevent pregnancy.