Endocrine System Role of the Endocrine System

Hormones: Types

Transport of Hormones

Interaction of Hormones with Target Cells

Effects of Hormones on Target

Control Mechanisms of Endocrine Glands

Endocrine Organs

• Pituitary (Anterior and Posterior)

• Thyroid

• Parathyroids

• Adrenals (Cortex, Medulla)

• Pancreas

• Gonads

Ovaries

Testes

The Endocrine System A more broad-based and long-lasting

communication system than the nervous system

Uses chemical messages (hormones) that are released into the blood

Hormones control several major processes

• Reproduction

• Growth and development

• Mobilization of body defenses

• Maintenance of much of homeostasis

• Regulation of metabolism

Types of Hormones Protein-based hormones

Steroid hormones

Prostaglandins and catecholamines

Insulin Growth hormone

Hormones as Chemical Messengers

Endocrine gland (source)

Target organs or glands

Hormones move through the bloodstream to target organs

Hormone Interaction with Target Cells Hormones bind to receptors sticking out from the plasma membrane of

target cells or within target cells

growth factor insulin epinephrine

Hormones

Examples of receptors found in the plasma membrane of cells

Receptors

Effects Caused by Hormones Changes in electrical state of the cell,

stimulating change

Causes enzymes to be made, changing metabolic abilities of target cell

Turn on or off enzymes that alter metabolism inside cell

Stimulate cell division and multiplication

Turn on certain genes

Control Mechanisms of Endocrine Glands

Hormonal: Chemical stimulus (i.e. endocrine

glands are activated by other hormones)

Humoral/Blood-Based: Changing blood levels of

certain ions stimulate hormone release

Neural: Nerve impulses stimulate hormone release; most are under

control of the sympathetic nervous system

Location of Major Endrocrine Organs

Figure 9.3

Pituitary Gland

glandular tissue nervous tissue

blood portal system

Nervous system that hormones can drip down on

Flip and enlarge

Hormones of the Anterior Pituitary Six anterior pituitary hormones

• Two affect non-endocrine targets

• Four stimulate other endocrine glands (tropic hormones)

Characteristics of all anterior pituitary hormones

• They are proteins (or peptides)

• They act through second-messenger systems

• They are regulated by hormonal stimuli, mostly negative feedback

Hormones of the Anterior Pituitary

Increases bone and

skeletal massCauses

milk secretion in breasts

Causes follicle and sperm maturation,

ovulation and testosterone production

Stimulates thyroid

hormone secretion

Causes aldosterone,

glucocorticoid, or androgen

release

Hormones of the Posterior Pituitary

Inhibits diuresis (urine production) and

increases blood pressure

Stimulates uterine muscle contraction in labor and intercourse; causes milk

ejection

Thyroid Gland

Figure 9.6

Thyroid hormone

Controls rate of cellular respiration. All body cells are targets.

Calcitonin

Decreases blood calcium levels by causing bone calcium deposition. Made by parafollicular cells.

Consists of two lobes and a connecting isthmus

Thyroid Hormone Lack of Dietary Iodine: Goiter

Hyposecretion of thyroxine

( hypothyroidism in adults)

Hyperthyroidism (Grave's disease)

Calcitonin (Calcium deposition) Decreases blood

calcium levels by causing its deposition on bone

Antagonistic to parathyroid hormone

Produced by C (parafollicular) cells

Figure 9.9

Parathyroid Glands (Calcium removal)

Parathyroid hormone

1. Stimulates osteoclasts to remove calcium from bone

2. Stimulates the kidneys and intestine to absorb more calcium

3. Raises calcium levels in the blood

Found on posterior surface of thyroid

Adrenal Glands Two parts that act as if

separate glands

• Cortex – outer glandular region in three layers

• Medulla – inner neural tissue region

Sits on top of the kidneys

Ad-renal both mean “upon or

Epi-nephros next to the kidney”&

Adrenal Hormones and Their Locations

Adrenal Cortex

Outer portion produces mineralocorticoids like aldosterone

Middle layer produces glucocorticoids like cortisone and cortisol

Innermost layer produces androgens like estrogens and testosterone

Medulla produces catecholoamines like epinephrine and norepineprhine

Adrenal Cortex (Outer Portion)

Aldosterone release causes salt and water retention, increasing blood pressure

Hormones of the Innermost Cortex Layer Sex hormones (steroids)

• Produced in the inner layer of the adrenal cortex

• Androgens (male) and some estrogen (female) -- both produced regardless of gender

• Hypersecretion causes masculinization (regardless of gender) - most obvious effects in females

• Hyposecretion causes Addison's disease

Hormones of the Adrenal Medulla Produces two similar hormones

(catecholamines)

• Epinephrine

• Norepinephrine

These hormones prepare the body to deal with short-term stress

Sympathetic system stimulates catecholamine release in fight or flight: increased heart rate, blood pressure, blood gluocose, respiratory rate

Pancreatic Islets The pancreas is a mixed gland

The islets of the pancreas produce hormones

• These hormones are antagonists that maintain blood sugar homeostasis

Pancreatic Islets

Figure 9.13

Insulin

Allows glucose to cross plasma membranes into cells from beta cells (hypoglycemic hormone)

Glucagon

Allows glucose to enter the blood from alpha cells (hyperglycemic hormone)

Pancreatic Hormones and Blood Sugar

Figure 9.14

Pineal Gland Found on the third

ventricle of the brain

Secretes melatonin

• Helps establish the body’s wake and sleep cycles

• May have other as-yet-unsubstantiated functions

Hormones of the Ovaries Estrogens

• Produced by Graafian follicles or the placenta

• Stimulates the development of secondary female characteristics

• Matures female reproductive organs

• Helps prepare the uterus to receive a fertilized egg

• Helps maintain pregnancy

• Prepares the breasts to produce milk

Hormones of the Ovaries Progesterone

• Produced by the corpus luteum

• Acts with estrogen to bring about the menstrual cycle

• Helps in the implantation of an embryo in the uterus

Hormones of the Testes

Interstitial cells of testes are hormone-producing

Produce several androgens

Testosterone is the 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 the small intestine

Parts of the stomach

Thymus

Kidneys

Heart

Many other areas have scattered endocrine cells

Developmental Aspects of the Endocrine System Most endocrine organs operate smoothly until old age

Menopause is brought about by lack of efficiency of the ovaries

Problems associated with reduced estrogen are common

Growth hormone production declines with age

Many endocrine glands decrease output with age