Endocrine System

Chp 13

Hormones:

• Produced by endocrine glands [e.g. pituitary]

• Circulate in the blood stream

1. Steroids - lipid soluble

2. Nonsteroids - not lipid soluble

• Often interact with nervous system

• Act on specific cells [target cells] in the body

Endocrine System: Regulates body

functions with Hormones

• Access to every cell

• Each hormone acts only on specific target cells

• Target cells have receptors for specific hormones

• Endocrine control slower than nervous system

• Endocrine & nervous systems interact

Endocrine System Characteristics

Steroid Hormone Action on a Target Cell

Figure 13.2

Steroid Hormones:

• Lipid soluble, chemically derived from cholesterol

• Enter target cells

• Activate specific genes to produce specific proteins

• Slower acting than nonsteroid hormones, minutes to hours

Classification of Hormones: Steroid

Nonsteroid Hormone Action on a Target Cell

Figure 13.3

Nonsteroid hormones:

• Water soluble

• Bind to receptors on target cell membranes

• Work through intermediate mechanisms to activate existing enzymes

• Faster action than steroid hormones, seconds to minutes

Classification of Hormones: Nonsteroid

Role of Negative Feedback Loops

Figure 13.4

Posterior pituitary gland:

Connection to hypothalamus: hormones made in hypothalamus, stored in posterior pituitary

Hormones: nonsteroidal operate here

1. Antidiuretic hormone (ADH): conserves water in kidneys, regulates water balance in body

2. Oxytocin: causes uterine contractions during labor & milk ejection through neuroendocrine reflex

Hypothalamus and the Posterior Pituitary Gland

Anterior pituitary gland:

Connection to hypothalamus: releasing and inhibiting hormones from hypothalamus travel to pituitary through pituitary portal system

Hormones: nonsteroidal operate here

1. ACTH- stimulates adrenal cortex

2. TSH- acts on thyroid gland

3. FSH, LH, Prolactin- related to control of reproductive cycles and lactation

4. Growth Hormone- widespread effects on body

Hypothalamus & the Anterior Pituitary Gland

1. Hypersecretion of ADH - excessive water retention

2. Diabetes Insipidus - hyposecretion of ADH, inability to conserve water appropriately

3. Gigantism- hypersecretion of growth hormone

4. Pituitary Dwarfism- hyposecretion of growth hormone

Pituitary Disorders

Hormones secreted by islets of Langerhans are

Nonsteroidal:

1. Glucagon - raises blood sugar

2. Insulin- lowers blood sugar

Pancreas: Endocrine Functions include

Roles of Insulin and Glucagon in Regulating Blood Glucose

Figure 13.9

Adrenal cortex - secretes steroid hormones

Produces small amounts of estrogen & testosterone

Produces:

• Cortisol [regulates blood glucose]

• Aldosterone [regulates sodium & potassium]

Adrenal Glands: 2 small endocrine glands located

just above kidneys

Adrenal medulla- secretes nonsteroid hormones

Secretion: stimulated by sympathetic nervous system

Nonsteroidal hormones that control metabolism, blood pressure & heart rate

1. Epinephrine [adrenaline]

2. Norepinephrine

They both enhance function of sympathetic

nervous system (Fight or Flight Response)

Adrenal Glands: Medulla

• Secretion: mediated through hypothalamus-pituitary secretions

• Secretes Steroidal hormones:

• Thyroxine (T4) and Triiodothyronine (T3) - both regulate production of ATP from glucose, affects metabolic rate

• Calcitonin: lowers blood calcium levels

Thyroid Gland

• Secretion: response to lowered blood calcium levels

• Hormone: Parathyroid hormone (PTH), nonsteroidal

• Removes calcium and phosphate from bone

• Increases absorption of calcium by the digestive tract

• Increases renal retention of calcium and excretion of phosphate

Parathyroid Glands

Hormone secreted = Testosterone (steroidal)

Functions:

1. Regulates development and normal functioning of sperm, male reproductive organs, male sex drive

2. Development of male secondary sex characteristics

Testes

Hormones (steroidal) & functions:

1. Estrogen- initiates development of secondary sex characteristics, regulates menstrual cycle

2. Progesterone - regulates menstrual cycle

Ovaries

1. Histamine - inflammation

2. Prostaglandins - local control of blood flow

3. Growth factors - local acting/ mitotic activity

Other Chemical Messengers

Thyroid Disorders:

1. Hypothyroidism - underactivity of thyroid

• Children: slows body growth, brain development & delays puberty

• Adults: causes edema, weight gain, lethargy, low body temp.

2. Hyperthyroidism: [Graves Disease]

• Overactive thyroid

• Causes- Increased BMR, hyperactivity, nervousness, weight loss

Disorders of the Endocrine System

Adrenal Gland Disorders:

1. Addison’s Disease: failure of adrenal cortex to secrete sufficient cortisol & aldosterone

• Lowers blood glucose & sodium

• Symptoms: Chronic fatigue, weakness, weight loss & abdominal pain

2. Cushing’s Syndrome: excessive cortisol produced

• High blood glucose & reduced muscle mass

• Retension of too much salt & water

• Symptoms: weakness & fatigue, edema, high blood pressure