The Endocrine Systemchapter 16

Endocrine System: Definitions• Endocrine – releasing substances into

blood– Endo = within or internal

– Contrast with Exocrine – releasing substances outside the body

• Hormone – a chemical that influences the function of a remote tissue (acts at a distance)

Endocrine System: Overview

9 glands in total

Endocrine glands

1. pituitary

2. thyroid

3. parathyroid

4. adrenal

5. pineal

6. thymus

Mixed glands

A. produce both hormones and exocrine products

1. pancreas

2. gonads

B. produce hormones and has neural functions

1. hypothalamus

Pineal glandHypothalamus

Pituitary gland

Thyroid gland

Parathyroid glands(on dorsal aspectof thyroid gland)

Thymus gland

Adrenal glands

Pancreas

Ovary(female)

Testis(male)

Hormones• How they work

– Regulate the metabolic function of other cells

– Have lag times ranging from seconds to hours

– Tend to have prolonged effects– Are classified as amino acid-based

hormones, or steroids

2 M ain Types of Hormones• Amino acid based

– Water-soluble – Do not enter the cell– e.g., insulin, norepinepherine, epinephrine

• Steroids – Lipid soluble– Act intracellularly and activate genes– e.g., testosterone, estrogen, cortisol

Mechanism of Hormone Action• Act on receptors in the plasma membrane

• Amino acid–based hormones– e.g., epinephrine- binds to smooth muscle cells in blood

vessels - causing contraction

• Direct gene activation• Steroid hormones, thyroid hormones

– e.g., growth hormone - stimulates cells to increase in size and divide

• The precise response depends on the type of the target cell

• The ONLY tissue to respond is the Target Tissue (may be very specific (1) tissue, or multiple tissues)

Hormone Blood Concentrations• Concentrations of circulating hormone reflect:

– Rate of release– Speed of inactivation and removal from the body

• Hormones are removed from the blood by:• Degrading enzymes• The kidneys• Liver enzyme systems

Hypothalamic Control• Hypothalamus “releasing hormones” and

“inhibiting hormones” tells of central control by brain– GHRH (growth hormone RH) and GHIH (growth

hormone IH) control GH from Ant. Pituitary– PRH (prolactin RH) and PIH control PL from Ant.

Pit.– TRH thyrotropin RH – release of TSH from Ant.

Pit.– CRH corticotropin releasing hormone – release

of hormones from adrenal cortex Stress– GnRH gonadotropin RH – release of gonadal

hormones from Ant. Pit. LH and FSH

Pituitary (Hypophysis)

• Pituitary gland – two-lobes – secretes 9 major hormones

• Connected to the hypothamus by – Posterior Lobe

• Neurohypophysis – neural tissue) and the infundibulum• Receives, stores, and releases hormones from the

hypothalamus

– Anterior Lobe• Adenohypophysis – made up of glandular tissue • Synthesizes and secretes a number of hormones

Pituitary (Hypophysis)

Figure 16.6

Anterior Pituitary Hormones• regulate other endocrine glands

• GH – growth hormone• TSH – thyroid stimulating hormone• ACTH – adrenocorticotrophic hormone• FSH – follicle stimulating hormone• LH – luteinizing hormone• PRL - prolactin

(latter 3 are called gonadotropins)

Growth Hormone (GH)

• Underproduction in children dwarfism

• Overproduction in children gigantism

• Overproduction in adults acromegaly

Posterior Pituitary Hormones

• Posterior pituitary– stores antidiuretic hormone (ADH) and oxytocin– ADH and oxytocin are synthesized in the

hypothalamus

• Oxytocin stimulates smooth muscle contraction in breasts and uterus– “cuddle hormone”

• Both are amino acid based – Receptor location?

• both exocrine and endocrine cells,

• Acinar cells enzyme-rich juice used for digestion (exocrine product)

• Pancreatic islets (islets of Langerhans) produce hormones (endocrine products)

• The islets contain two major cell types:– Alpha () cells that produce glucagon– Beta () cells that produce insulin

Pancreas

Regulation of Blood Glucose Levels

Figure 16.18

• hyperglycemic

glucagon glucose uptake

• hypoglycemic

insulin glucose release

• Results from hyposecretion or hypoactivity of insulin

• The three cardinal signs of DM are:– Polyuria – huge urine output– Polydipsia – excessive thirst– Polyphagia – excessive hunger and food

consumption

Diabetes Mellitus (DM)

Thyroid Gland

• thyroid hormonemetabolism, BP,

growth– T3 (10x)– T4

• calcitoninresponse to rising blood calcium – inhibit gut absorption and kidney reabsorption of Ca++

Thyroid Disorders• Hypothyroidism

– Thyroid gland defect, inadequate TSH, lack of iodine• Low metabolic rate, feeling chilled• Goiter formation ( if cause is lack of

iodine)

• Cretinism = Hypothyroidism in infants• Stunted growth, low mentality• can be prevented by hormone

replacement therapy

Grave’s Disease– Hyperthyroidism

• Autoimmune disease- body attacks and stimulates the thyroid cells - increased thyroid hormone

• High BMR, Weight loss, Increased heart rate, Protrusion of the eyeballs, goiter

– Treated by surgical removal of the thyroid gland

Parathyroid Glands

• PTH (parathormone) – response to falling

calcium in blood – promotes gut absorption and kidney reabsorption of Ca++

– Question:• what two hormones

regulate calcium in blood?

• Adrenal glands – cope with stressful events

• Structurally and functionally, they are two glands in one– Adrenal cortex – glandular tissue – Adrenal medulla – neural tissue

that acts as part of the SNS

Adrenal (Suprarenal) Glands

Adrenal Cortex Hormones• Aldosterone - dehydration

– causes kidney to reabsorb Na+ reabsorb water

– stimulated by angiotensin (remember Renin)

• Cortisol - stress– increases blood glucose levels & reduces

edema of tissues– prolonged high levels changes in neural

and circulatory function, depressed bone/cartilage growth, suppressed immune response

Adrenal Cortex Hormones• Androgens (masculinizing hormones)

– most important is testosterone• the onset of puberty• secondary sex characteristics• sex drive in females

– testosterone can be converted to estrogen in females after menopause

Disorder• Addison’s disease

– Hyposecretion of the adrenal cortex• Deficiency in cortisol and aldosterone• Low BP• Hypoglycemia

• Cushings disease– Hypersecretion of adrenal cortex (tumor of the

adrenal cortex)• Hyperglycemia• “buffalo hump” (fat on upper back)

Adrenal Medulla• secretes the catecholamines

– epinephrine – norepinephrine

• “Fight or Flight” secretion causes:– blood glucose levels to rise– blood vessels to constrict– faster heart rate– blood diversion to brain, heart, and skeletal

muscle

Adrenal Medulla• Epinephrine is the more potent

stimulator of the heart and metabolic activities

• Norepinephrine is more influential on peripheral vasoconstriction and blood pressure

Stress and the Adrenal Gland

Figure 16.16