Transcript Lecture 18, The Endocrine System - Websupport1

Anatomy & Physiology
SIXTH EDITION
Lecture 18, The Endocrine
System
Lecturer: Dr. Barjis
Room: P313
Phone: (718) 260-5285
E-Mail: [email protected]
The Endocrine System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Frederic H. Martini
Fundamentals of
Learning Objectives
• Compare the major chemical classes and general
mechanisms of hormones.
• Describe the location and structure of the
pituitary gland, and explain its structural and
functional relationships with the hypothalamus.
• Describe the location and structure of each of the
endocrine glands.
Learning Objectives
• Identify the hormones produced by each of the
endocrine glands and specify the functions of
those hormones.
• Describe the functions of the hormones produced
by the kidneys, heart, thymus, testes, ovaries and
adipose tissue.
• Explain how hormones interact to produce
coordinated physiological responses.
Intercellular Communication
Endocrine versus Nervous system
•
Nervous System
•
Nervous system performs short term
crisis management
•
The nervous system sends electrical
messages to control and coordinate the
body
•
Nerve impulse is delivered by the axon
of a nerve cell called neuron
•
Endocrine System
•
Endocrine system regulates long term
ongoing metabolic activity
•
The endocrine system uses chemicals
messenger called hormones to
“communicate”.
• Hormones alter metabolic
activities of tissues
•
A hormone is secreted by a group of
specialized cells called gland
•
Hormones are transported by the blood
vessels
•
Paracrine communication involves
chemical messengers between cells
within one tissue
Endocrine system
• Includes all cells and endocrine tissues that produce hormones or
paracrine factors
• Following are important endocrine glands
• Hypothalamus
• Pituitary gland
• Pineal Gland
• Thyroid gland
• Parathyroid gland
• Thymus
• Adrenal Gland
• Gonads (testes/ovaries)
• Pancreatic Islet
• Heart
• Kidney
• Digestive Tract
The Endocrine System
Hormone structure
• Based on their chemical structure hormones are
classified into three general classes (groups) of
hormones.
• 1) Amino acid derivatives hormones e.g. epinephrine
• Structurally similar to amino acids
• 2) Peptide hormones e.g. insulin
• Chains of amino acids
• 3) Lipid derivatives hormones e.g. eicosanoids and
steroid hormones (prostaglandin is an example of a
steroid hormone)
A Structural Classification of Hormones
Hormones Transportation
• Hormones can be
• Freely circulating
• Rapidly removed from bloodstream
• Bound to transport proteins e.g. albumin or
globulin
Mechanisms of hormone action
• Each hormone’s shape is specific and can be
recognized by the corresponding target cells
• The binding sites on the target cells are called
hormone receptors.
• Receptors for peptide hormones, are located
on the surface of cell membranes because they
can not cross the membrane to enter the cell
• Thyroid and steroid hormones can cross the
membrane and bind to receptors in the
cytoplasm or nucleus
G Proteins and Hormone Activity
•
Hormones that
can not cross the
membrane (e.g.
Peptide
hormones) bind
to the receptor on
the surface of the
cell
•
Binding of
hormones to the
receptor activate
secondary
messenger (in
this figure
binding of
hormone
activates G
protein, and
activated G
protein activates
adenylcyclase
or activate PDE
or activates PLC
Hormone Effects on Gene Activity
•
Hormones that
can cross the
membrane (e.g.
steroid
hormones) bind
to the receptor
inside the cell, at
the cytoplasm, or
they will enter the
nucleus and bind
to the receptor at
the nucleus and
initiate
transcription)
Control of endocrine activity
• Hypothalamus regulates the activity of the
nervous and endocrine systems
• Hypothalamus secrets regulatory hormones
(releasing hormones and inhibiting hormones)
that control the activity of the pituitary gland
• Releasing/inhibiting hormones secreted by the
hypothalamus either stimulate or inhibit
activity of pituitary gland
Three Methods of Hypothalamic Control over
the Endocrine System
The Pituitary Gland
• The pituitary gland is called the “master gland”
but it is under the control of the hypothalamus.
• Hypothalamus and pituitary gland control many
other endocrine functions.
• Pituitary Gland releases nine important peptide
hormones
• All nine bind to membrane receptors and use
cyclic AMP as a second messenger
• Pituitary gland is divided into posterior and
anterior lobe
The Anatomy and Orientation of the Pituitary
Gland
The anterior lobe (adenohypophysis)
Hormones of the adenohypophysis
• Anterior lobe of pituitary gland produces 7
hormones
• 1) Thyroid stimulating hormone (TSH)
• TSH triggers the release of thyroid hormones by the thyroid
glands
• Thyrotropin releasing hormone promotes the release of TSH
• 2) Adrenocorticotropic hormone (ACTH)
• ACTH stimulates the release of glucocorticoids by the adrenal
gland
• Corticotrophin releasing hormone causes the secretion of ACTH
• 3) Follicle stimulating hormone (FSH)
• FSH stimulates follicle development and estrogen secretion in
females and sperm production in males
The anterior lobe (adenohypophysis)
• 4) Leutinizing hormone (LH)
• LH causes ovulation and progestin (progesterone) production in
females and androgen (testosterone) production in males
• Gonadotropin releasing hormone (GNRH) promotes the secretion
of FSH and LH
• 5) Prolactin (PH)
• PH stimulates the development of mammary glands and milk
production
• 6) Growth hormone (GH or somatotropin)
• GH stimulates cell growth and replication through release of
somatomedins or IGF
• Growth-hormone releasing hormone
(GH-RH)
• Growth-hormone inhibiting hormone
(GH-IH)
• 7) Melanocyte stimulating hormone (MSH)
• Stimulates melanocytes to produce melanin
The posterior lobe of the pituitary gland
(neurohypophysis)
• The posterior lobe of the pituitary gland secretes two
hormones: Antiduretic Hormone and Oxytocin.
• 1) Antidiuretic hormone (ADH)
• Decreases the amount of water lost at the
kidneys
• Elevates blood pressure
• 2) Oxytocin
• Stimulates contractile cells in mammary glands
• Stimulates smooth muscle cells in uterus
The thyroid
• Thyroid gland is located near the thyroid cartilage of the larynx
• The two lobes of thyroid gland is connected by an isthmus
• Microscopically it has 2 distinct population of cells: Flicular Cell
(produce thyroid hormone) and C cell (produce calcitonin)
• Thyroid gland release several hormones such as thyroxine (T4) and
triiodothyronine (T3)
• Thyroid hormones (T4 and T3) are transported by to thyroid binding
globulins (TBG), and albumin
• Functions of Thyroid hormones include:
• Increasing ATP production, when bound to mitochondria.
• Activating genes that control energy utilization, when bound to
receptors
• Exert a calorigenic effect
• C cells of thyroid gland produce calcitonin
• Calcitonin helps to regulate calcium concentration in body fluids
The Thyroid Gland
Parathyroid glands
• Four parathyroid glands embedded in the
posterior surface of the thyroid gland
• Chief cells produce parathyroid hormone (PTH)
in response to lower than normal calcium
concentrations
• Parathyroid hormones plus calcitriol are primary
regulators of calcium levels in healthy adults
The Homeostatic Regulation of Calcium Ion
Concentrations
•
When calcium levels decrease in the
blood, parathyroid glands produce
PTH
•
•
PTH increase blood calcium level
by:
1.
Releasing stored calcium
from the bones
2.
Stimulating production of
calcitriol at the kidney.
Calcitriol increases
absorption of calcium by
the digestive system
3.
Enhance reabsorption of
calcium by the kidneys
When calcium levels increase in the
blood, thyroid glands produce
calcitonin.
•
Calcitonin decreases blood
calcium level by:
1.
Increasing excretion of
calcium by the kidneys
2.
Increase calcium deposition
in the bones
3.
Stop osteoclast
The Adrenal Glands
Adrenal cortex
• Manufactures steroid hormones derived from
cholesterol (corticosteroids).
• Corticosterioid hormones are divided into 3
functional groups
• Mineralocorticoids (Aldosterone)
• Regulate mineral and salt balance by reninangiotensis-aldosterone system
• Glucocorticoids (cortisol and cortisone)
• Regulate glucose levels i.e. they increase
gluconeogenesis and decrease protein
synthesis
• Decrease inflammation response
• Androgens also called sex hormones
The Adrenal Glands
Adrenal medulla
• Responsible for flight-or-fight response
• Produces epinephrine and norepinephrine
Pineal gland
• Contains pinealocytes
• Synthesize melatonin
• Suggested functions include inhibiting
reproductive function, protecting against damage
by free radicals, setting circadian rhythms
(biological clock)
The Pancreas
The pancreatic islets
• Clusters of endocrine cells within the pancreas
called Islets of Langerhans or pancreatic islets
• Alpha cells secrete glucagons
• Glucagon raises blood glucose by increasing the rates
of glycogen breakdown and glucose manufacture by
the liver
• Beta cells secrete insulin
• Insulin lowers blood glucose by increasing the rate of
glucose uptake and utilization
• Delta cells secrete GH-IH
• F cells secrete pancreatic polypeptide
Diabetes
• Type I – Insulin dependent diabetes
• Caused by autoimmune destruction of beta
cells
• Type II – non insulin dependent diabetes
• Caused by body resisting the effects of insulin
at its receptor.
• Symptoms: Polyuria (inreased frequency of
urination), polydipsia (increased thirst)
The Regulation of Blood Glucose Concentrations
The kidneys
• Produce calcitriol and erythropoietin (EPO) and the enzyme rennin
• Calcitriol = stimulates calcium and phosphate ion absorption along
the digestive tract
• EPO stimulates red blood cell production by bone marrow
• Renin converts angiotensinogen to angiotensin I
• Angiotensin I is converted to angiotensin II at the lungs
• Agiotensin II:
1.
Stimulates production of aldosterone by the adrenal glands
2.
Stimulates release of ADH by the pituitary gland
3.
Promotes thirst
4.
Elevates blood pressure
Endocrine Functions of the Kidneys
Endocrine Functions of the Kidneys
The heart, The intestines and the Thymus
• The Heart
• Specialized muscle cells produce natriuretic peptides in
response to high blood pressure
• Natriuretic peptide generally has the opposite actions
of angiotensin II
• The Intestine
• Produce hormones important to the coordination of
digestive activities
• The Thymus
• Produces thymosins
• Help develop and maintain normal immune defenses
The gonads
• Interstitial cells of the testes produce testosterone
• Most important sex hormone in males
• In females, oocytes develop in follicles
• Follicle cells produce estrogens
• After ovulation, the follicle cells form corpus
luteum. Corpus luteum releases a mixture of
estrogens and progesterone
Hormones and growth
• Normal growth requires the interaction of several
endocrine organs
• Six hormones are important
• GH
• Thyroid hormones
• Insulin
• PTH
• Calcitriol
• Reproductive hormones
Adipose tissues secrete
• Leptin, a feedback control for appetite
• Resistin, which reduces insulin sensitivity
Hormones and behavior
• Many hormones affect the CNS
• Changes in the normal mixture of hormones
significantly alters intellectual capabilities,
memory, learning and emotional states