Two - Endocrine System and Renal Assessment

Maintaining Homeostasis in the Endocrine System

Nervous System	Endocrine System
Responds quickly (milliseconds)  to stimulus through electrical signals with neurons to alter activities of an effector (specific muscle or gland)	Responds more slowly (minutes) to stimulus through hormones into bloodstream (blood plasma) to alter activities of an effector (any cell with an appropriate hormone receptor)

Hormones are produced and secreted by various endocrine glands located in body;

• Pineal gland

• Hypothalamus

• Pituitary gland

• Thyroid gland

• Parathyroid glands

• Thymus

• Adrenal glands

• Pancreas

• Gonads (ovary and testis)

Three Main Categories of Stimuli:

1. Hormonal stimulus - one hormone stimulates secretion of another

2. Humoral stimulus - changes in blood ion or nutrient levels, e.g. glucose, Ca2+, Na+, K+

3. Neural stimulus - signals from nervous system

Chemical Classes of Hormones

Steroid Hormones	Amino Acid-Based Hormones
Made from cholesterol Lipid-soluble, can easily diffuse across plasma membrane Bind to receptors inside cell (intracellular receptors)	Vary in size - can be single amino acids, peptides, proteins Lipid-insoluble, cannot easily diffuse across membrane Bind to receptors embedded in plasma membrane (plasma membrane receptors)

Hormone Actions and Effects

The binding of a hormone to its intracellular or plasma membrane receptor activates the target cell response.

Effects of Hormone Action:

• Activating or deactivating enzymes

• Changing permeability of plasma membrane

• Stimulation protein synthesis

• Inducing cell secretory activity

• Stimulation cell division

Hormones Alter Target Cell Activity To:

• Control rate of chemical reactions

• Facilitate transportation of substances in and out of cells

• Regulate fluid and electrolyte balance, blood pressure, reproductive functions, development and growth

• Maintain homeostasis

Posterior Pituitary Hormones

Does not produce its own hormones; secretes two hormones produced by the hypothalamus (oxytocin and ADH)

Antidiuretic Hormone (ADH) Stimulus: Na+ increases, or BP decreases Main Action: Targets kidneys: dilutes blood plasma, restores blood volume and maintains blood volume/pressure

Oxytocin Stimulus: Uterine stretch during labour, suckling action from breastfeeding Main Action: Targets uterus: stimulates contractions in labour Targets mammary glands: stimulates milk ejection

Anterior Pituitary Hormones

Hypothalamic neurons produce/secrete releasing and inhibiting hormones that regulate (stimulate or inhibit) the secretion of anterior pituitary hormones.

• Thyrotropin-releasing hormone (TRH) 

• Corticotropin-releasing hormone (CRH) 

• Growth hormone-releasing hormone (GHRH) 

• Growth hormone-inhibiting hormone (GHIH) 

• Gonadotropin-releasing hormone (GnRH) 

• Prolactin-inhibiting hormone (PIH)

Gonadotropins - GnRH

Stimulus for Secretion Secretion of FSH and LH Main Actions FSH Ovaries - development of egg containing follicles. production/secretion of oestrogen Testes - regulate sperm production LH Ovaries - ovulation. production/secretion of progesterone (mainly) and oestrogen Testes - production/secretion of testosterone

Prolactin - PRL

Stimulus for Secretion Secretion of PRL. decreased PIH (Prolcatin Inhibiting-Hormone) = increased PRL Main Actions Targets mammary glands to stimulate milk production in women

Adrenocorticotrophic Hormone - CRH

Stimulus for Secretion Secretion of ACTH Main Actions Targets adrenal cortex (outer part of adrenal glands) and stimulated to secrete hormone cortisol

Thyroid-Stimulating Hormone - TRH

Stimulus for Secretion Secretion of TSH Main Actions Target thyroid gland to secrete thyroid hormones T3 and T4

Growth Hormone - GH

Stimulus for Secretion Growth hormone-releasing hormone (GHRH) - stimulates secretion of GH Growth hormone-inhibiting hormone (GHIH or Somatostatin) - inhibits secretion of GH Main Actions Promotes growth of body tissues, skeletal muscle and bone Stimulated cells in liver, skeletal muscles and bones to secrete insulin-like growth factors (IGFs) = actions required for growth, e.g. cell division/protein synthesis Clinical Connection Hyposecretion = dwarfism Hypersecretion = gigantism (children) & acromegaly (adults)

Thyroid Hormones (TSH) - Thyroid and Parathyroid Glands

Stimulus for Secretion TSH stimulates TH secretion by thyroid gland Main Actions Targets every cell Increases basal metabolic rate Increases body heat production Increases HR and force of contraction by increasing number of β -adrenergic receptors on cardiac muscle cells Promotes growth of muscles and bones Promotes nervous system development Clinical Connection Deficiencies during fetal development/infancy/ childhood lead to mental retardation and stunted bone growth Hyposecretion in adulthood = low BMR, HR, blood pressure, cold intolerance, muscular weakness, weight gain Hypersecretion in adulthood = high BMR, increased body temp, rapid HR, high blood pressure, weight loss

Calcitonin - Thyroid and Parathyroid Glands

Stimulus for Secretion Secreted by parafollicular cells of thyroid gland when Ca2+ levels increase above normal range Main Actions Targets bone Inhibiting activity of osteoclasts (bone cells that release stored calcium into blood) Stimulate calcium uptake from blood into bone

Parathyroid Hormone - Thyroid and Parathyroid Glands

Stimulus for Secretion PTH secreted by parathyroid glands when Ca2+ levels decrease below normal range Main Actions Targets bone, kidneys, small intestines Clinical Connection Hypoparathyroidism = hypocalcaemia (low blood Ca2+ levels) Hyperparathyroidism = excessive resorption of bone matrix & release of stored calcium into blood

Erythropoietin (EPO) - Kidneys

Stimulus for Secretion EPO secreted by kidneys when blood oxygen levels drop below normal range (hypoxemia) Main Action Targets bone marrow for blood production

Cortisol (stress hormone) - Adrenal Glands

Stimulus for Secretion Anterior pituitary hormones ACTH stimulated secretion of cortisol from adrenal cortex Main Action Resists stressors by increasing blood glucose, fatty acids, amino acid levels by; Stimulating skeletal muscles to break down muscle proteins into amino acids Stimulating liver to produce glucose from amino acids and glycerol Stimulating adipose tissue to break down stored fat into fatty acids Clinical Connection Inhibitory effect on body’s immune system Treats patients with autoimmune and chronic inflammatory disorders

Aldosterone - Adrenal Glands

Stimulus for Secretion Secretion from adrenal cortex Increase in blood K+ levels Angiotensin II Main Action Maintains K+ and NA+ levels through kidneys Clinical Connection Hypersecretion = high blood pressure, oedema, hypernatremia, hypokalemia

Adrenaline & Noradrenaline - Adrenal Glands

Stimulus for Secretion From adrenal medulla controlled by preganglionic neurons of sympathetic division during stressful environments Main Action Enhance/prolong fight-or-flight response Increase heart rate Dilate bronchioles Increase sweat gland activity Dilate blood vessels Constrict blood vessels Dilate pupils Decrease digestive and urinary functions

Insulin - Pancreas

Stimulus for Secretion Secreted by pancreatic β (beta) cells when blood volume is high Main Actions High blood glucose → pancreatic beta cells stimulate to secrete insulin → uptake glucose from bloodstream Clinical Connection Diabetes Type 1 - inadequate insulin production due to destruction of pancreatic beta cells Type 2 - occurs when body cells become non-responsive to insulin

Glucagon - Pancreas

Stimulus for Secretion Secreted by pancreatic α (alpha) cells when blood glucose levels are low Main Actions Low blood glucose → pancreatic alpha cells are stimulated to secrete glucagon → releases glucose into the blood (targets liver)

Oestrogen (estrogen)

Stimulus for Section Anterior pituitary hormones FHS & LH stimulate ovaries Main Actions Targets female reproduction organs (vagina, uterus, uterine tubes) Promote growth and maturation and regulate menstrual cycle Development of secondary sex characteristics; enlarged breasts, feminisation of skeleton (hips widening), increased fat storage

Progesterone

Stimulus for Section Anterior pituitary hormone LH stimulated ovaries Main Actions “Pregnancy hormone” Prepares uterus for pregnancy and maintains pregnancy Regulates menstrual cycle

Testosterone

Stimulus for Section Anterior pituitary hormone LH stimulated testes Main Actions Targets male reproductive organs (ducts, glands, penis, scrotum, testes) Promote growth and maturation and stimulate sperm production Development of male secondary sex characteristics; increased muscle mass, bone growth, growth of body hair