ch 17 the endocrine system

Ch 17

The Endocrine System

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

Organs and Tissues of the Endocrine

System

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


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


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.


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

Negative Feedback Loop

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

Endocrine Reflexes

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

.

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

Feedback Control of Endocrine Secretion

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)

Pituitary Gland

Pituitary Hormones and Their Targets.

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

The Thyroid Gland

The Thyroid Gland.

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

Thyroid Follicles: The Regulation of Thyroid Secretion.

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

The Parathyroid Glands.

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

Parathyroid Glands

Homeostatic Regulation of Calcium Ion Concentrations.

17-6 Suprarenal Glands

.

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 Cortex

The Suprarenal Gland.

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

The Endocrine Pancreas

Pancreas

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

Pancreas

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 Functions of the Kidneys: The Production of Calcitriol

Vit D3

Endocrine Functions of the Kidneys: Overview of the Renin-angiotensin System


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


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

Hormone Interactions

The General Adaptation Syndrome.

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

Aging

Hormone Changes

Can alter intellectual capabilities, memory, learning,

and emotional states

Affect behavior when endocrine glands are over-

secreting or under-secreting

Aging

Causes few functional changes

Decline in concentration of

Growth hormone

Reproductive hormones

ch 17 the endocrine system

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