ch 17 the endocrine system
TRANSCRIPT
Introduction to the Endocrine System
The Endocrine System
Regulates long-term, general processes and
responses
Growth
Development
Reproduction
Uses chemical messengers called hormones to relay
information and instructions between cells
17-1 An Overview of the Endocrine System
Endocrine Communication
Endocrine cells release chemicals (hormones) into
bloodstream and other bodily fluids
Alters metabolic activities of many tissues and organs
simultaneously
Target Cells
Are specific cells that possess receptors needed to
bind and “read” hormonal messages
Hormones -Stimulate synthesis of enzymes or structural
proteins, increase or decrease rate of synthesis, or turn
17-2 Hormones
Can be divided into four types
Amino acid derivatives/ peptides
Catecholamines -(NH2)
Protein hormones
Lipid derivatives- steroids
Circulate freely or bound to transport proteins
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hormones
Figure 18–2 A Structural Classification of Hormones
Mechanisms of Hormone Action
Hormone Receptor (for amino acids/peptides-
polar!)
Is a protein molecule to which a particular molecule
binds strongly
Responds to several different hormones
Different tissues have different combinations of
receptors
Presence or absence of specific receptor determines
hormonal sensitivity
Mechanisms of Hormone Action
Catecholamines, Proteins and Peptide Hormones
Are not lipid soluble - unable to penetrate plasma
membrane- Polar Molecules
Bind to receptor proteins at outer surface of
plasma membrane (extracellular receptors) Bind
to receptors in plasma membrane
Use intracellular intermediary to exert effects
- uses second messenger
– may act as enzyme activator, inhibitor, or cofactor
– results in change in rates of metabolic reactions
Mechanisms of Hormone Action- cell
Membrane Receptors
When hormone (ligand) meets specific
receptor:
-Process of Amplification/ Transduction
binding of a small number of hormone
molecules to membrane receptors
Leads to thousands of second messengers in
cell
Magnifies effect of hormone on target cell
Second Messengers
G- proteins - activated when hormone binds to
receptor at membrane surface and changes concentration
of second messenger activate
Second Messengers
-Cyclic-AMP (cAMP), Cyclic-GMP (cGMP) with Calcium
ions
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mechanisms of Hormone Action
Figure 18–3 G Proteins and Hormone Activity.
Mechanisms of Hormone Action-
Nonpolar Molecules
Lipid Derivatives (steroids and thyroid hormone)
Alter rate of DNA transcription in nucleus
Change patterns of protein synthesis
Directly affect metabolic activity and structure of
target cell
Pass directly through membrane- receptor is
intracellular and outside the nucleus.
Receptor and hormone move into nucleus and
transcription begins.
Mechanisms of Hormone Action
Down-regulation
Presence of increasing hormone triggers decrease in
number of hormone receptors
When levels of particular hormone are high, cells
become less sensitive
Up-regulation
Absence of a hormone triggers increase in number of
hormone receptors
When levels of particular hormone are low, cells
become more sensitive
Regulation of Hormone Secretion
Endocrine Reflexes
Functional counterparts of neural reflexes
In most cases, controlled by negative
feedback mechanisms
Stimulus triggers production of hormone whose
effects reduce intensity of the stimulus
Endocrine Reflexes
Simple Endocrine Reflex
Involves only one hormone
Controls hormone secretion by the heart, pancreas,
parathyroid gland, and digestive tract
Complex Endocrine Reflex
Involves
One or more intermediary steps
Two or more hormones
Hypothalamus involved
17.3 The Pituitary Gland and
Hypothalamus
Called hypophysis
Lies within sella turcica- A dural sheet that
locks pituitary in position
Isolates it from cranial cavity
Hangs inferior to hypothalamus
Connected by infundibulum
Pituitary Gland
Median Eminence -Swelling near attachment of infundibulum
Site where hypothalamic neurons release regulatory
factors-
into interstitial fluids
through special
-fenestrated capillaries
Hypothalamus (Command Center)
Portal System - Blood vessels link two capillary networks
Entire complex is portal system
Ensures that regulatory hormones reach intended target cells
before entering general circulation
Two Classes of Hypothalamic Regulatory Hormones
Releasing hormones (RH)
Stimulate synthesis and secretion of one or more hormones
at anterior lobe
Inhibiting hormones (IH)
Prevent synthesis and secretion of hormones from the
anterior lobe
Rate of secretion is controlled by homeostatic feedback
Pituitary Gland
Releases nine important peptide hormones
Hormones bind to membrane receptors
Use cAMP as second messenger
Anterior: GH (also called somatotropin), TSH,
Prolactin, ACTH, FSH, LH
Intermediate: MSH
Posterior: oxytocin, ADH
Pituitary Gland
Anterior lobe (called adenohypophysis)
Hormones “turn on” endocrine glands or support other organs
Subdivided into regions:
1. Pars distalis
2. Pars intermedia
Pituitary Gland
Posterior lobe (called neurohypophysis)
Contains unmyelinated axons of hypothalamic
neurons
Nuclei manufacture:
Antidiuretic hormone (ADH)
Oxytocin (OXT)
17-4 The Thyroid Gland
Lies anterior to thyroid cartilage of larynx Consists of two lobes connected by narrow isthmus
Thyroid follicles-make thyroglobulin
Hollow spheres lined by cuboidal epithelium
Cells surround follicle cavity that contains viscous colloid
17-4 The Thyroid Gland
Thyroglobulin (Glycoprotein)
Synthesized by follicle cells
Secreted into colloid of thyroid follicles
Molecules contain the amino acid tyrosine
Binding of TSH- cells actively transport iodine into follicle where
Thyroxine (T4) and Triiodothyronine (T3) are formed and released
back into the bloodstream.
T3 and T4 are metabolic hormones and influence metabolic resting
rate. -Necessary for protein synthesis, cellular respiration, etc.
The Thyroid Gland
Hormones
TSH -Absence causes thyroid follicles to become inactive
Neither synthesis nor secretion occurs
Binds to membrane receptors- Activates key enzymes in thyroid
hormone (T3 and T4) production
T3 and T4 Enter target cells by transport system
Affect most cells in body:
In children, essential to normal development of
Skeletal, muscular, and nervous systems
Cell consumes more energy resulting in increased heat
generation and strong, immediate, and short-lived increase in
rate of cellular metabolism
The Thyroid Gland
C (Clear) Cells of the Thyroid Gland
Produce calcitonin (CT)
Helps regulate concentrations of Ca2+ in body
fluids- when
Ca2+ levels in blood
High (hypercalcemia)
17-5 Parathyroid Glands
Embedded in posterior surface of thyroid
gland
Parathyroid hormone (PTH)
Produced by chief cells
In response to low concentrations of Ca2+
(hypocalcemia)
Figure 18–12
Parathyroid Glands
Four Effects of PTH when hypocalcemic:
It stimulates osteoclasts
Accelerates mineral turnover and releases Ca2+ from bone
It inhibits osteoblasts
Reduces rate of calcium deposition in bone
It enhances reabsorption of Ca2+ at kidneys, reducing
urinary loss
It stimulates formation and secretion of calcitriol at
kidneys
Effects complement or enhance PTH
Enhances Ca2+, PO43- absorption by digestive tract
Figure 18–12
17-6 Suprarenal (Adrenal) Glands
Subdivided into
Superficial suprarenal cortex (divided into zona)
Stores lipids, especially cholesterol and fatty acids
Manufactures steroid hormones: minerocorticoids
(aldosterone); glucocorticoids (cortisol); androgens
Collectively- adrenocortical steroids (corticosteroids) and
Inner suprarenal medulla
Secretory activities controlled by sympathetic division of ANS
Produces epinephrine (adrenaline) and norepinephrine
Metabolic changes persist for several minutes
Suprarenal Cortex (Controlled by ACTH)
Subdivided into three regions:
1. Zona glomerulosa -Outer region of suprarenal cortex
Produces mineralocorticoids aldosterone:
– stimulates conservation of sodium ions and elimination of potassium
ions- increases sensitivity of salt receptors in taste buds
Secretion responds to:
– drop in blood Na+, blood volume, or blood pressure
– rise in blood K+ concentration
2. Zona fasciculate -produces glucocorticoids- cortisol –glucose metabolism-
Liver converts cortisol to cortisone -
Has inhibitory effect on production of corticotropin-releasing hormone (CRH)
in hypothalamus (ACTH in adenohypophysis)
3. Zona reticularis- Produces androgens (sex hormones) secondary source.
Suprarenal Medulla
Contains two types of secretory cells that produce
catecholamines in response to sympathetic
nervous system stimulation:
One produces epinephrine (adrenaline)
– 75 to 80% of medullary secretions
The other produces norepinephrine (noradrenaline)
– 20 to 25% of medullary secretions
17-7 Pineal Gland
Lies in posterior portion of roof of third
ventricle
Contains pinealocytes
Synthesize hormone melatonin
Functions of Melatonin
Inhibiting reproductive functions
Protecting against damage by free radicals
Setting circadian rhythms
17-8 Gonadal and Placental Hormones
Testes (Gonads)
Produce androgens in interstitial cells
Testosterone is the most important male hormone
Secrete inhibin in nurse (sustentacular)
cells
Support differentiation and physical maturation of
sperm
Gonadal and Placental Hormones
Ovaries (Gonads)
Produce estrogens
Principle estrogen is estradiol
After ovulation, follicle cells
Reorganize into corpus luteum
Release estrogens and progestins, especially
progesterone
17-9 Endocrine Pancreas
Lies between -Inferior border of stomach and proximal portion of small intestine
Contains exocrine (digestion) and endocrine cells
Endocrine Pancreas
Consists of cells that form clusters known as pancreatic islets, or
islets of Langerhans
Alpha cells produce glucagon
Beta cells produce insulin
Delta cells produce peptide hormone identical to GH-IH
F cells secrete pancreatic polypeptide (PP) (appetite)
Pancreas
Blood Glucose Levels
When levels rise
Beta cells secrete insulin, stimulating transport of
glucose across plasma membranes
When levels decline
Alpha cells release glucagon, stimulating glucose
release by liver
17-10 Endocrine Tissues of Other
Systems Many organs of other body systems have secondary
endocrine functions
Intestines (digestive system)- gastrin, CCK
Kidneys (urinary system)- renin, erythropoeitin
Heart (cardiovascular system)- atrial natriuretic (ANP)
Thymus thrymosin (immunity)
Skin (cholecalciferol to calcitriol (liver) to
VitaminD3)
Adipose – leptin, adiponectin, resistin
Endocrine Tissues of Other Systems
Intestines
Produce hormones important to coordination of
digestive activities
Kidneys
Produce the hormones calcitriol and erythropoietin
(RBC production)
Produce the enzyme renin (angio-tensin-
aldosterone) reabsorption of sodium and water.
Endocrine Tissues of Other Systems
Heart
Produces natriuretic peptides (ANP and BNP)
When blood volume becomes excessive
Action opposes angiotensin II
Resulting in reduction in blood volume and blood pressure
Thymus
Produces thymosins (blend of thymic hormones)
That help develop and maintain normal immune defenses
Endocrine Tissues of Other Systems
Adipose Tissue Secretions
Leptin
Feedback control for appetite
Controls normal levels of GnRH, gonadotropin
synthesis
Resistin
Reduces insulin sensitivity
General Adaptation Syndrome (GAS)
& Homeostasis GAS -Also called stress response
How body responds to stress-causing factors
Is divided into three phases:
1. Alarm phase 2. Resistance phase 3. Exhaustion phase
Figure 18–18
17-11 Development and Aging
Hormones Important to Growth
GH
In children- Supports muscular and skeletal development
In adults -Maintains normal blood glucose concentrations- Mobilizes
lipid reserves
Thyroid hormones
Insulin
PTH
Calcitriol
Reproductive hormones
Development and Adult
Thyroid Hormones
If absent during fetal development or for first
year
Nervous system fails to develop normally
Mental retardation results
If T4 concentrations decline before puberty
Normal skeletal development will not continue
Development and Adult
Insulin
Allows passage of glucose and amino acids across
plasma membranes
Parathyroid Hormone (PTH) and Calcitriol
Promote absorption of calcium salts for deposition in
bone
Inadequate levels causes weak and flexible bones
Development
Reproductive Hormones
Androgens in males, estrogens in females
Stimulate cell growth and differentiation in
target tissues
Produce gender-related differences in
Skeletal proportions
Secondary sex characteristics