LESSON 9: ENDOCRINE SYSTEM

 A stimulus or low hormone levels in the

blood trigger the release of hormone
 Hormone release stops once an appropriate
level in the blood is reached

Hormonal Stimuli of Endocrine Glands

 Endocrine glands
are activated by
other hormones

Introduction:
 The endocrine system includes the organs of
the body that secrete hormones directly into
body fluids such as blood
 Regulates chemical reaction in cells and
therefore control functions of the organs,
tissues, and other cells
 Second messenger system of the body

 Uses chemical messages (hormones) that are

released into the blood Humoral Stimuli of Endocrine Glands

 Hormones control several major  Changing

processes : blood levels for
1. Reproduction certain ions
2. Growth and Development stimulate
3. Mobilization of body defenses hormone
4. Maintenance of much of homeostasis release
5. Regulation of metabolism

 Hormones are…
 Chemical messengers
 Secreted by endocrine glands or tissues into
blood
 Travel everywhere blood goes
 Affect only target cells, cells with receptors
 May affect very distant organs or cells

The Chemistry of Hormones

 Amino-acid based hormones:
 Proteins
 Peptides
 Amines
 Steroids – made from cholesterol
 Prostaglandins – made from highly active Neural Stimuli of Endocrine Glands
lipids  Nerve impulses – stimulate hormone release
 Most are under the control of the
Mechanisms of Hormone Action SYMPATHETIC NERVOUS SYSTEM
 Hormones affect only certain tissues or
organs (target cells or organs) Overview of the Endocrine System: Hormones
 Target cells must have specific protein and Endocrine Glands
receptors
 Hormone binding - influences the working Exocrine Glands
of cells - Uses ducts to release secretions to tissue

Control of Hormone Release Endocrine Glands

 Hormone levels in the blood are maintained - Ductless, release into blood
by NEGATIVE FEEDBACK - Other organs not usually considered
endocrine glands:
 LESSON 9: ENDOCRINE SYSTEM

 Brain and heart, releasing important

substances

Comparison of the Nervous and Endocrine

Systems
Endocrine System
 Chemical signals only
 Slower to respond and stop
 Hormones go everywhere
 Adapts relatively slowly
 Sometimes widespread effects
Growth Hormone
Nervous System  General metabolic hormone
 Chemical and electrical signals  Major effects are directed to growth of skeletal
 Responds and stops quickly muscles and long bones
 Targets specific organs  Causes amino acids to be built into proteins
 Adapts quickly  Causes fats to be broken down for a source of
 Usually local effects energy

Location of Major Endocrine Organs Functions of Other Anterior Pituitary Hormones

 Prolactin (PRL)
 This stimulates and maintains milk
production following childbirth
 Function in males is unknown

 Adrenocorticotropic Hormone (ACTH)

 Regulates endocrine activity of the adrenal
cortex

 Thyroid-stimulating Hormone (TSH)

 Influences growth and activity of the thyroid

 Gonadotropic Hormones
 They regulate hormonal activity of the
gonads

 Follicle-stimulating hormone (FSH)

 Stimulates follicle development in
ovaries
 Stimulates sperm development in testes

 Luteinizing Hormone (LH)

Pituitary Gland  Triggers ovulation
 Causes ruptured follicle to become the
 Size of a grape corpus luteum
 Hangs by a stalk from the hypothalamus  Stimulates testosterone production in
males
 Sphenoid bone – protects pituitary gland
 Referred to as INTERSTITIAL CELL-
 Has 2 functional lobes: STIMULATING HORMONE (ICSH)
 Anterior Pituitary – glandular tissue
 Posterior Pituitary – nervous tissue Pituitary – Hypothalamus Relationship
 Release of hormones is controlled by releasing
Hormones of the Anterior Pituitary and inhibiting hormones produced by the
 Six anterior pituitary hormones hypothalamus
 2 affect non-endocrine targets  Hypothalamus – produces two hormones that
 4 stimulate other endocrine glands are transported to neurosecretory cells of the
posterior pituitary
 Characteristics of all anterior pituitary  The posterior pituitary is not strictly an
hormones: endocrine gland, but does release hormones
 Proteins (or peptides)
 Act through second-messenger systems Hormones of the Posterior Pituitary
 Regulated by hormonal stimuli, mostly  Oxytocin
NEGATIVE FEEDBACK - Stimulates contraction of the uterus during labor
- Causes milk ejection

 Antidiuretic Hormone (ADH)

- Can inhibit urine production
 LESSON 9: ENDOCRINE SYSTEM

- In large amounts, causes vasoconstriction

leading to increased blood pressure Hyperthyroidism
(vasopressin)  Increased metabolism
 Weight loss, increased appetite, nervousness
Thyroid Gland  Higher temp. and pulse
 Found at the base of the throat  Warm, flushed skin
 Consists of 2 lobes and a connecting isthmus  Graves’ disease (leads to goiter)
 Produces 2 hormones
 Thyroid hormone Parathyroid Glands
 Calcitonin  Tiny masses on the posterior of the thyroid
 Secrete PARATHYROID HORMONE
 Stimulate osterclasts to remove calcium
from bone
 Stimulate the kidneys and intestine to
remove more calcium
 Raise calcium levels in the blood

Thyroid Hormone
 Major metabolic hormone
 Composed of 2 active iodine-containing hormones
 Thyroxine (T4) – secreted by thyroid fossicles
 Triodothyronine (T3) – conversion of T4 at
target tissues
Adrenal Glands
 2 Glands:
Calcitonin
 Cortex – outer glandular region in three layers
 Medulla – inner neural tissue region
 Sits on top of the kidneys

Hormones of the Adrenal Cortex

 Decreases blood calcium levels by causing its
deposition on bone
Mineralocorticoids (mainly aldosterone)
 ANTAGONISTIC to parathyroid hormone
 Produced in outer adrenal cortex
 Produced by C (parafollicular) cells  Regulate mineral content in blood, water, and
electrolyte balance
Abnormalities of Thyroid Gland  KIDNEY – target organ
 RENIN AND ALDOSTERONE – stimulates the
Hypothyroidism production
 DECREASED metabolism  ATRIAL NATRIURETIC PEPTIDE – inhibits
 Weight gain, reduced appetite, fatigue production
 Low temp. and pulse
 Dry, cold skin
 Myxedema in adults Glucorticoids (including cortisol and cortisone)
 Cretinism in infants
 LESSON 9: ENDOCRINE SYSTEM

 Produced in the middle layer of the adrenal

cortex
 Promote normal cell metabolism
 Help resist long-term stressors
 Released in response to increased blood levels
of ACTH

Sex Hormones
 Produced in the inner layer of the adrenal cortex
 Androgens – male
 Estrogen – female

Pancreatic Hormones and Blood Sugar

Hormones of the Adrenal Medulla

 Produces 2 similar hormones (catecholamines)
 Epinephrine
 Norepinephrine

 These hormones prepare the body to deal with

short-term stress

Role of Hypothalamus and Adrenal Glands in Stress

Response
 Diabetes Mellitus
 Causes: too little insulin or faulty insulin
receptors
 Symptoms: exaggerated appetite, excess
urine, dehydration, thirst, fatigue
 TYPE I – Insulin dependent (daily
injections required)
 TYPE II – Insulin independent

Pineal Gland
 Found on the third ventricle of the brain
 Secretes melatonin
 Helps establish the body’s wake and sleep
cycle
 May have other as-yet-unsubstantiated
functions

Pancreatic Islets

 Pancreas – mixed gland

 The islets of the pancreas produce hormones
 Insulin – allows glucose to cross plasma
membranes into cells from beta cells
 Glucagon – allows glucose to enter the blood
from alpha cells

 These hormones are antagonists that maintain

blood-sugar homeostasis
 LESSON 9: ENDOCRINE SYSTEM

Thymus
 Located posterior to the sternum
 Largest in infants and children
 Produces THYMOSIN
 Matures some types of white blood cells Developmental Aspects of the Endocrine System
 Important in developing immune system
 Most endocrine organs operate smoothly until
Hormones of the Ovaries old age
 Menopause – brought about by lack of
 ESTROGENS efficiency in the ovaries
- Stimulates the development of secondary female  Problems with reduced estrogen are common
characteristics  Growth hormone declines with age
- Matures female reproductive organs  Many endocrine glands decrease output with age
- Helps prepare the uterus to receive a fertilized
egg
- Helps maintain pregnancy
- Prepares the breasts to produce milk

 PROGESTERONE
- Acts with estrogen to bring about the menstrual
cycle
- Helps in the implantation of an embryo in the
uterus

Endocrine Function of the Placenta

 Produces hormones that maintain the pregnancy
 Some hormones play a part in the delivery of a
baby
 Produces HCG in addition to estrogen,
progesterone, and other hormones

Hormones of the Testes

 Interstitial cells of testes are hormone-producing
 Produce several androgens
 TESTOSTERONE – most important
androgen
 Responsible for adult male secondary sex
characteristics
 Promotes growth and maturation of male
reproductive system
 Required for sperm cell production

Other Hormone-producing Tissues and Organs

 Parts of small intestine
 Parts of stomach
 Kidneys
 Heart
 Many other areas have scattered endocrine cells