Hormones and the Endocrine System

Chapter 45

ENDOCRINE SYSTEM

• Endocrine system – chemical signaling by hormones

• Endocrine glands – hormone secreting organs

• Hormones – chemical signals that are secreted into body fluids (usually blood) and communicate regulatory messages throughout body– Regulate growth, development,

reproduction, metabolism, and behavior

Figure 45.2 Hormonal regulation of insect development (Layer 3)

CHEMICAL SIGNALING• Reception – a receptor detects a

signal (usually signal binds to receptor)

• Transduction – binding of signal to receptor changes receptor’s shape which initiates chemical changes (often several steps)

• Response – final transduced signal triggers a specific cell response

Figure 45.3 Mechanisms of chemical signaling: a review

• Different cells will have different receptors.

• This means that one hormone only affects cells that have receptors for that specific hormone.

• However, different cells may have different receptors for same hormone which can then cause different affects.

Figure 45.4 One chemical signal, different effects

HUMAN ENDOCRINE GLANDS

• Hypothalamus• Pineal gland• Pituitary gland• Thyroid gland• Parathyroid glands• Thymus• Adrenal glands• Pancreas• Ovary or testis (gonads)

Figure 45.5 Human endocrine glands surveyed in this chapter

PANCREAS

• Secretes insulin and glucagon from the islets of Langerhans in pancreas

• Insulin and glucagon are antagonistic hormones.

• Metabolic balance requires a minimum of 90 mg glucose/100 ml blood.

• When blood glucose rises over 90mg/100ml: – Insulin lowers blood glucose by

stimulating body cells to take in glucose. – Insulin also slows glycogen breakdown

in liver.

• Before blood glucose reaches 90mg/100ml:–Glucagon signals liver cells to break down glycogen into glucose and release to blood

–Signals liver cells to convert amino acids and glycerol into glucose and release to blood

Figure 45.12 Glucose homeostasis maintained by insulin and glucagon

Diabetes Mellitus• Caused by a deficiency of insulin or

loss of response in target tissues• Result is high blood glucose levels – so

high that a diabetic’s urine contains glucose

• More glucose in urine means more water needed in urine = thirst

• Cells don’t get the glucose they need so they break down fat instead, which forms harmful, acidic metabolites.

• Type I diabetes mellitus– Insulin dependent– Autoimmune disease where

immune system attacks pancreas ( cells) and cannot make insulin

– “Juvenile” (adults too)– Inheritance may play a minor

role– Potentially caused by infections

• Type II diabetes mellitus– Non-insulin dependent– Often inherited (although related to poor

diets and lack of exercise)– Either insulin deficient or lack of response

in target cells– Accounts for 90% of all diabetics– Gastric by-pass surgery (duodenum and

jejunum removal) ends diabetes in most obese patients

• Gestational diabetes – happens to pregnant women (may be from hormones from placenta causing insulin resistance in mom)

Figure 45.14 Stress and the adrenal gland

SHORT TERM STRESS• Stressful stimuli cause

hypothalamus to activate adrenal gland via a nerve to secrete epinephrine (adrenaline) and norepinephrine (noradrenaline).

• Multiple effects:– Glycogen broken down to

glucose; increases blood glucose– Increased blood pressure and

stroke volume– Increased breathing rate (dilates

bronchioles)

– Increased metabolic rate–Change in blood flow patterns leading to decreased digestion and kidney activity

– Increase rate of oxygen delivery to cells (used to stimulate heart)

Figure 45.12 The synthesis of catecholamine hormones

LONG TERM STRESS• Hypothalamus secretes a releasing

hormone that activates the anterior pituitary to release ACTH (adrenocorticotropic hormone)

• When ACTH reaches the adrenal gland via blood it stimulates the gland to secrete corticosteroids.

• Two main types of corticosteroids – Glucocorticoids (ex. Cortisol)– Mineralcorticoids (ex. Aldosterone)

• Glucocorticoids– Promotes glucose synthesis from

noncarbs like proteins – used for fuel– Break down skeletal muscle for

protein source– Suppress some parts of immune

system (ex. Anti-inflammatory)

• Mineralcorticoids– Aldosterone stimulates kidneys to

reabsorb water and sodium so blood volume and therefore blood pressure increases