David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.blu
C – Il corpo umano
Endocrine System
Endocrine System
• What are hormones and how do they
work?
• How do the nervous and endocrine
systems interact?
• What are the major mammalian
endocrine glands and hormones?
• What happens when a gland
malfunctions?
Endocrine System - What are hormones and how do they work?
Hormones are chemical signals secreted
by cells of the endocrine system.
Endocrine cells: cells that secrete
hormones.
Target cells: cells that have receptors for
the hormones.
Endocrine System - What are hormones and how do they work?
Circulating hormones diffuse into the
blood and can activate target cells far
from the site of release.
• Paracrine hormones: affect only target
cells near the site of release.
• Autocrine hormones: affect the cells
that released the hormones.
Endocrine System - What are hormones and how do they work?
Chemical signaling systems (part 1)
Endocrine System - What are hormones and how do they work?
Chemical signaling systems (part 2)
Endocrine System - What are hormones and how do they work?
Some endocrine cells are single cells
(e.g., in the digestive tract).
• Endocrine glands: aggregations of
secretory cells; hormones are secreted
to the extracellular space.
• Exocrine glands: ducts carry products
to the outside of the body.
Endocrine System - What are hormones and how do they work?
Three types of hormones:
• peptides or polypeptides - water-soluble,
transported in blood but not across
membranes;
• steroid hormones - lipid-soluble, must be
bound to carrier proteins to be carried in
blood;
• amine hormones - derivatives of tyrosine.
Endocrine System - What are hormones and how do they work?
Hormone receptors:
• lipid soluble hormones - receptors are
inside the cell;
• water-soluble hormones cannot readily
pass cell membrane - receptors are on
the outside.
Endocrine System - What are hormones and how do they work?
The endocrine system (part 1)
Endocrine System - What are hormones and how do they work?
The endocrine system (part 2)
Endocrine System - What are hormones and how do they work?
Multiple feedback loops control hormone secretion
Endocrine System - What are hormones and how do they work?
Epinephrine (adrenalin) stimulates “Fight or Flight”
responses
Endocrine System - How do the nervous and endocrine systems interact?
The pituitary gland is attached to the
hypothalamus of the brain.
Posterior pituitary secretes
neurohormones (synthesized by
neurons in the hypothalmus): oxytocin
and ADH.
Endocrine System - How do the nervous and endocrine systems interact?
The posterior pituitary releases neurohormones
Endocrine System - How do the nervous and endocrine systems interact?
The anterior pituitary secretes:
• tropic hormones - control other endocrine
glands;
• growth hormone - promotes growth;
• prolactin - breast development and milk
production;
• enkephalins and endorphins - natural
opiates.
Endocrine System - How do the nervous and endocrine systems interact?
The anterior pituitary produces hormones
Endocrine System - How do the nervous and endocrine systems interact?
Hormones from the hypothalamus control
the anterior pituitary.
The hypothalamus produces releasing
hormones—carried to the anterior
pituitary by portal blood vessels.
Negative feedback loops control hormone
secretion from the anterior pituitary.
Endocrine System - How do the nervous and endocrine systems interact?
The thyroid gland consists of many follicles (A)
Thyroxine is produced by
the follicles
Endocrine System - How do the nervous and endocrine systems interact?
The thyroid gland consists of many follicles (B)
Endocrine System - What are the major mammalian endocrine glands and hormones?
Thyroxine regulates cell metabolism.
Anterior pituitary secretes thyrotropin (TSH),
which activates the follicles to produce
thyroxine.
The thyroid gland also produces calcitonin.
Regulation of calcium levels in the blood is
controlled by calcitonin, parathyroid hormone,
and vitamin D.
Endocrine System - What are the major mammalian endocrine glands and hormones?
The thyroid gland produces thyroxine (T4) and
triiodothyronine (T3).
Endocrine System - What are the major mammalian endocrine glands and hormones?
Hormonal regulation of calcium (part 1)
Endocrine System - What are the major mammalian endocrine glands and hormones?
Hormonal regulation of calcium (part 2)
Endocrine System - What are the major mammalian endocrine glands and hormones?
The parathyroid glands secrete parathyroid
hormone (PTH).
PTH raises blood calcium levels:
• stimulates osteoclasts;
• stimulates kidneys to reabsorb calcium;
• activates vitamin D, which stimulates digestive tract
to absorb calcium.
Vitamin D (calciferol) is produced by skin cells from
cholesterol, by UV light.
Endocrine System - What are the major mammalian endocrine glands and hormones?
Insulin binds to receptors on target cells
and allows uptake of glucose.
• Lack of insulin: type I diabetes.
• Lack of insulin receptors on target cells:
type II diabetes.
Endocrine System - What are the major mammalian endocrine glands and hormones?
Islets of Langerhans: clusters of
endocrine cells in the pancreas.
• b cells produce insulin.
• a cells produce glucagon: stimulates liver
to convert glycogen back to glucose.
• d cells produce somatostatin: inhibits
release of both (also released by the
hypothalamus).
Endocrine System - What are the major mammalian endocrine glands and hormones?
Adrenal gland: two glands, on top of the
kidneys.
Adrenal medulla: epinephrine and
norepinephrine.
On target cells: a-adrenergic and badrenergic receptors.
b-blockers block b-adrenergic receptors.
Endocrine System - What are the major mammalian endocrine glands and hormones?
The adrenal gland has an outer and an inner portion
Endocrine System - What are the major mammalian endocrine glands and hormones?
Adrenal cortex produces corticosteroids
from cholesterol:
• glucocorticoids - cortisol;
• mineralocorticoids - aldosterone;
• sex steroids.
Endocrine System - What are the major mammalian endocrine glands and hormones?
The corticosteroid hormones are built from cholesterol
Endocrine System - What are the major mammalian endocrine glands and hormones?
Aldosterone stimulates kidneys to retain sodium and
excrete potassium.
Cortisol mediates reaction to stress; cells not critical
for action decrease use of blood glucose; blocks
immune system reactions.
Cortisol release is controlled by corticotropin from the
anterior pituitary, in turn controlled by
corticotropin-releasing hormone from the
hypothalamus.
Stress response is turned off by negative feedback of
cortisol to brain.
Endocrine System - What are the major mammalian endocrine glands and hormones?
Gonads produce sex steroids:
• androgens - testosterone;
• estrogens - (estradiol) and
progesterone.
In development, sex hormones determine
whether fetus will become male or female.
Endocrine System - What are the major mammalian endocrine glands and hormones?
At puberty, production of sex hormones
increases.
Controlled by gonadotropins from the
anterior pituitary:
• luteinizing hormone (LH);
• follicle-stimulating hormone (FSH).
Endocrine System - What are the major mammalian endocrine glands and hormones?
The pineal gland produces melatonin
from tryptophan.
Melatonin is released in the dark; light
inhibits release.
Involved in photoperiodicity: seasonal
changes in light trigger physiological
changes.
Endocrine System - What happens when a gland malfunctions?
Goiter is an enlarged thyroid gland. It can
result from either hyperthyroidism
(thyroxine excess) or hypothyroidism
(thyroxine deficiency).
Epithelial cells produce excess
thyroglobulin and the follicles enlarge.