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Endocrine systemChapter 50
- endocrine system and the nervous system are two of the primary communicating and
coordinating systems in the body.
- Nervous system communicates through the nerves impulse
- Endocrine communicate through chemical substances known as Hormone
- Endocrine plays role of:
o Reproduction
o Growth
o Development
o Regulation of energy
- Endocrine gland includes:
o Hypothalamus
o Pituitary gland
o Thyroid
o Parathyroid
o Adrenal gland
o Pancreas
o Ovaries
o Testes
o Pineal gland
- Pineal gland secretes melatonin and involved in gonadal function and development
- Kidney secretes erythropoietin
- Heart secretes numerous natriuretic peptide
- Gastro-intestinal tract secreted peptide hormone[Gastrin]
Structure and functions of endocrine system:
Glands:
- Two types of glands:
o Exocrine
o Endocrine
Exocrine - Secretes substances into ducts that empty into the
body cavity or surfaces [skin]
- Example: salivary glands produces saliva, which
secreted through salivary duct in to mouth
Endocrine: - Secretes their substances directly into the blood, [NOT
INTO DUCTS]
Hormones:
- Hormone is a chemical substances synthesised and secreted by specific organ or tissue
- Common characteristics includes;
o secretion in small amounts at variable but predictable rates,
o circulation through the blood,
o binding to specific cellular receptors either in the cell membrane or within the
cell
,Endocrine system
o Lipid soluble hormone includes: steroids hormone [all hormones produced by
adrenal cortex and sex glands]
o Water soluble hormones all others
Regulation of hormonal secretions:
- These mechanisms stimulate or inhibits hormone synthesis and secretion includes:
o Simple feedback:
Regulations of hormone levels in the blood
Feedback is based on the blood level of a particulate substances
Negative feedback: respond by increasing or decreasing the secreting of a
hormone on the basis of feedback from various factor
Similar to “thermostat”
Example: of negative feedback
example of negative feedback is the relationship between calcium and
parathyroid hormone (PTH). Low blood levels of calcium stimulate the
parathyroid gland to release PTH, which acts on bone, the intestine,
and the kidneys to increase blood calcium levels. The increased blood
calcium levels then inhibit further PTH release
Positive feedback: mechanism increase the target organ beyond normal.
Example of positive feedback is {Oxytocin during childbirth
o Complex feedback
o Nervous system control
o Physiological rhythms
Hypothalamus: {PART OF THE BRAIN]
- Hypothalamus and pituitary gland is one of the most aspects of the endocrine system
- Pituitary is referred as the “MASTER GLAND “most of its functions rely on an
interrelationship with the hypothalamus
- Hypothalamus and pituitary gland integrate communication between the nervous and
endocrine
- The important groups of hormone from the hypothalamus are:
o Realising hormones
o Inhibiting hormones
- The function of these hormones is to either stimulate [release] and inhibits the secrete
of hormones form the anterior pituitary
Hormones of the hypothalamus:
The following hormones from the hypothalamus target the anterior pituitary.
Realising hormones
*Corticotrophin-releasing hormone (CRH)
• Gonadotropin-releasing hormone (GnRH)
• Growth hormone–releasing factor (GHRH), or somatotropin-releasing hormone
• Prolactin-releasing hormone (PRF)
• Thyrotropin-releasing hormone (TRH)
Inhibiting hormones
,Endocrine system
*Prolactin-inhibiting hormone (PIH)
• Somatostatin (inhibits growth hormone release)
- The hypothalamus also contains neurons, which receive input from the brain stem and
limbic system
- facilitate the coordination of the endocrine system, the autonomic nervous system, and
the expression of complex behavioral responses, such as anger and feelings of fear and
pleasure.
Pituitary gland
- also called hypophysis
- very small in size [like pea]
- located under hypothalamus
- its consist of two parts:
o anterior pituitary
o posterior
- hormone secreted form each of these pituitary lobes serves different functions
Anterior pituitary gland
- account 80% of gland by weight
- its regulated hypothalamus thought release and inhibiting hormones
[communicate throughout capillaries system of hypothalamus]
- tropic hormones: controls the secretion of the hormones by other glands
- Growth hormones: effects all body tissue of skeletal muscles, long bone, role
metabolism of protein, fat and carbohydrates
- Prolactin: stimulates the breast development necessary for lactation after
childbirth. Also known as Lactogenic hormone
Posterior pituitary Gland
- Is composed of nerve tissue and essentially extension of the hypothalamus
- Communication between hypothalamus and posterior pituitary gland occurs
through nerve tract
- These hormones secreted by posterior pituitary gland
o Antidiuretic hormones [ADH] also known as Vasopressin
o Oxytocin
-
Thyroid gland:
- Located in anterior portion of the neck in front of trachea
- It regulated by TSH from the anterior pituitary glad
- The three hormone produced and secreted by thyroid glad are ;
o Thyroxine [T4}
o Triiodothyronine {T3}
o Calcitonin
, Endocrine system
- Major function of thyroid gland is the production, storage and release of the thyroids
hormone T4 and T3.
- Functions - Regulation - Function
of T3, T4 and
Calcitonin
T4 and T3 - T4 and T3 levels are - Regulate protein, fat, and
controlled by carbohydrate catabolism in all cells
thyroid-stimulating - Regulate metabolic rate of all cells
- hormone; released - Regulate body heat production
in response to - Serve as insulin antagonists
metabolic demand - Maintain growth hormone secretion,
- Influences on skeletal maturation
amount secreted: - Affect central nervous system
- Gender development
- Pregnancy - Are necessary for muscle tone and
- Gonadal- and vigor
adrenocortical- - Maintain cardiac rate, force, and
increased steroids output
= ↑ levels - Maintain secretion of gastro-
- Exposure to intestinal (GI) tract
extreme cold = ↑ - Affect respiratory rate and oxygen
levels utilization
- Nutritional state - Maintain calcium mobilization
- Chemicals - Affect red blood cell production
- Growth hormone– - Stimulate lipid turnover, free fatty
inhibiting hormone acid release, and cholesterol
= ↓ levels synthesis
- Dopamine = ↓
levels
- Catecholamine’s =
↑ levels
Calcitonin - Elevated serum - Lowers serum calcium level by
calcium level— opposing bone-resorbing effects of
major stimulant for parathyroid hormone,
calcitonin - prostaglandins, and calciferous by
- Other stimulants: inhibiting osteoclastic activity
- Gastrin - Lowers serum phosphate levels
- Calcium-rich foods - Decreases calcium and phosphorous
(regardless of absorption in GI tract
serum calcium
levels)
- Pregnancy
- Lowered serum
calcium level—
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