Physiology endocrine system, Schemes and Mind Maps of Physiology

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Endocrine

system

• The endocrine system consists of endocrine glands that secrete chemicals called hormones.
• Endocrine glands are ductless (they do not have ducts to take their secretions to specific sites). Instead, hormones are secreted directly into capillaries and circulate in the blood throughout the body.

Chemistry of Hormones:

• With respect to their chemical structure, hormones may be classified into three groups: 1. Amines: these simple hormones are structural variations of the amino acid tyrosine. Examples: thyroxine, epinephrine and norepinephrine. 2. Proteins: these hormones are chains of amino acids. Insulin, growth hormone and calcitonin. Short chains of amino acids may be called peptides like Antidiuretic hormone and oxytocin. 3. Steroids: cholesterol is the precursor for the steroid hormones, which include cortisol, aldosterone , estrogen, progesterone , and testosterone.

Regulation of Hormone Secretion:

• The mechanism of regulation of secretion most endocrine hormones

is negative feedback mechanism,

• However, some hormones are regulated by positive feedback

mechanism

The Pituitary Gland (hypophysis)

1 - Antidiuretic Hormone (vasopressin)

The stimulus for secretion of ADH is:

1. Dehydration (through sweating or diarrhea)

2. Hemorrhage

Function:

1. Increases the reabsorption of water by kidney tubules → which decreases urine →increased blood volume.
2. Vasoconstriction, especially in arterioles → raise or at least maintain blood pressure. This function gives ADH its other name, vasopressin.
3. Decreases sweating.

1 - Antidiuretic Hormone (vasopressin)

Osmoreceptors (sensory

receptor) in the

hypothalamus detect the

increased “saltiness” of body

fluids → hypothalamus then

transmits impulses to the

posterior pituitary → increase

the secretion of ADH and

decrease the loss of more

water in urine.

2 - Oxytocin

(milk let-down reflex)

Sensory

impulses

Anterior Pituitary Gland

• They are in turn regulated by releasing hormones from the hypothalamus

rapidly stimulate the anterior pituitary, without having to pass through general

circulation..

1 - Growth hormone (somatotropin)

function

↑ amino acid uptake and protein synthesis ↑ use of fat for energy ↑ muscle and bone growth

1 - Growth hormone (somatotropin)

function

2 - Thyroid-Stimulating Hormone (TSH, thyrotropin)

Its secretion is

stimulated

when

metabolic rate

(energy

production)

decreases

3 - Adrenocorticotropic Hormone (ACTH) Its secretion is stimulated under physiological stress (injury, disease, exercise, or hypoglycemia (hungry is stress)) NEGATIVE FEEDBACK LOOP Corticotropin-releasing hormone (CRH) Adrenocorticotropic hormone (ACTH)