1. Chapter 16 – The Endocrine System

2. Endocrine system
Along with the nervous system, is responsible for homeostasis
Nervous system – fast-acting; short-term effects
Endocrine system – slow-acting; long-term effects
Utilizes chemical messengers called hormones
Gland types
Exocrine – have ducts
Endocrine – ductless when mature
Secrete into surrounding fluid and then enters bloodstream
Carried body-wide; affects distant tissues

3. Endocrine System

4. Structural classification of hormones
Amino acid derivatives
Hydrophilic
Peptide
Lipid derivatives
Hydrophobic
Steroids; sex hormones
Synthesized from cholesterol

6. Hydrophilic hormone receptors
Water soluble hormones can no diffuse through plasma membrane; receptors are on cell surface
Transmembrane proteins – span entire membrane
Hormone binds to receptor; receptor changes shape
Shape change activates G protein
Converts to an active form
Starts chain reaction that ultimately activates kinases
Kinases attach phosphate groups to molecules
This either activates the molecule or inactivates it, depending on the specific molecule

7. Hydrophobic hormone receptors
Fat soluble hormones can diffuse through plasma membrane
Receptors are located in cell’s interior (the cytoplasm)
Hormone-receptor complex enters nucleus and binds to DNA to affect gene expression

8. Control of hormone release
Endocrine reflexes
Humoral
Detects and responds to change in concentration of certain molecules
Neural
Signal from nervous system stimulates secretion
Hormonal
Some hormones target other endocrine glands
Tropic hormones (sometimes called trophic hormones)
All can be modified by nervous system

9. Pituitary gland (hypophysis)
Located in the sella turcica of the sphenoid bone
Attached to the hypothalamus by a stalk called the infundibulum
2 lobes
Posterior (neurohypophysis)
Anterior (adenohypophysis)

10. Pituitary gland hormones

11. Posterior pituitary (neurohypophysis)
Composed of neural tissue; stores and releases hormones produced by the hypothalamus
Antidiuretic hormone (ADH)
Increases water reabsorption
Aquaporins placed in the collecting ducts of the kidneys
Increases blood volume/pressure
Oxytocin (OXT)
Stimulates smooth muscle contractions
Uterine contractions during childbirth
Milk letdown in lactating females
Durng sexual arousal in males and females

12. Anterior pituitary (adenohypophysis)
Release or inhibition is controlled by hypothalamus
Growth hormone (GH)
Bones and skeletal muscles the major target tissues
Prolactin (PRL)
Stimulates milk production
Melanocyte-stimulating hormone (MSH)
Stimulates melanocytes in skin; contributes to skin pigmentation

13. Anterior pituitary (adenohypophysis)
Tropic hormones
Thyroid-stimulating hormone (TSH)
Thyroid gland
Adrenocorticotropic hormone (ACTH)
Adrenal cortex
Follicle-stimulating hormone (FSH)
Gonads to produce gametes
Leutinizing hormone (LH)
Stimulation of gonadal hormones

14. Thyroid gland On trachea, inferior to larynx Butterfly-shaped
2 lobes connected by isthmus

15. Thyroid gland microscopic anatomy
Follicle cells produce thyroglobin (a glycoprotein)
Simple cuboidal epithelium
Central cavity of follicles is filled with colloid – thyroglobulin with iodine atoms
Forms T3 and T4 hormones
Parafollicular cells (C cells) produce calcitonin

16. Thyroid hormones Thyroxine (T4) and Triiodothyronine (T3) Calcitonin
#4 and #3 refer to number of iodine atoms attached
Affects most cell in body
Increases basal metabolic rate and heat production
Aids in maintenance of blood pressure
Helps regulate growth and development
Calcitonin
Lowers blood calcium levels
Inhibits osteoclasts

17. Parathyroid glands Usually 4 on posterior thryoid Parathyroid hormone
Produced by chief cells
Increases blood calcium levels
Antagonistic to calcitonin
Stimulates osteoclasts
Increases reabsorption of calcium by kidneys
Kidney also converts vitamin D to its active form, which aids in calcium absorption in digestive system

18. Adrenal glands Also called suprarenal glands due to their location
Adrenal cortex (superficial) and adrenal medulla (deep)

19. Adrenal cortex microscopic anatomy
3 layers/zones (superficial to deep)
Zona glomerulosa
Produces mineralcorticoids
Zona fasciculata
Produces mainly glucocorticoids, some gonadocorticoids
Zona reticularis
Produces mainly gonadocortcoids, some glucocorticoids

20. Adrenal cortex hormones
Mineralcorticoids
Regulation of electrolytes in extracellular fluid
Aldosterone
Stimulates sodium reabsorption in distal convoluted tubules of kidneys
Glucocorticoids
Influence energy metabolism
Regulates blood glucose and blood pressure levels
Cortisol (hydrocortisone)
Gluconeogenesis – formation of glucose from non-carbohydrate sources
Excess of glucocorticoids results in oversuppression of inflammatory and anti-immune responses
Gonadocorticoids
Androgens
Male sex hormones
Converted to testosterone in males; estrogen in females
Estrogens

21. Adrenal medulla hormones
Autonomic nervous system
Epinephrine and norepinephrine
“Fight or flight” response
Blood glucose levels rise, increases heart rate, blood directed to cardiac and skeletal muscles
Epinephrine serves as a blood vessel contrictor and a bronchiole dilator

22. Pineal gland Located at roof of third ventricle in brain Melatonin
Concentration rises and falls within a 24 hour time period
Peaks at night – causes sleepiness
Affects biological clock/circadian rhythms

23. Pancreas Posterior to stomach Microscopic anatomy Acinar cells
Produce pancreatic secretions for digestive system
Islets of Langerhans
Alpha cells – produce glucagon
Beta cells – produce insulin

24. Pancreatic hormones Glucagon Insulin Increases blood glucose levels
Glycogenolysis
Breaks down glycogen to glucose
Gluconeogenesis
Synthesizes glucose from non-carbohydrate sources
Releases glucose from the liver
Insulin
Decreases blood glucose levels (antagonistic to glucagon)
Increases glucose transport into cells (primarily adipose and muscle)
Uses glucose for ATP production
Stores as glycogen
Excess stored as fat

25. Thymus Overlays heart Produces several peptide hormones
Thymosin, thymopoetin, thymic factor
Development/maturation of T lymphocytes

26. Gonadal hormones Hormones are steroids (fat-soluble) Ovaries (female)
Estrogen
Secondary sex characteristics
Maturation of reproductive organs
Progesterone
Along with estrogen:
Breast development and menstrual cycle regulation
Testes (male)
Testosterone
Production of sperm