1. Chapter 16 Endocrine System Lecture 13
Marieb’s Human
Anatomy and Physiology
Marieb w Hoehn
Chapter 16
Endocrine System
Lecture 13
Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1]
Slides 16 – 38; 50 min [Lecture 2]
118 min (38 slides plus review of course Web sites and syllabus)

2. Lecture Overview Overview of the Endocrine System
Control of Hormone Secretion
Hormone Chemistry and Actions
The Hypothalamus / Pituitary Gland
The Thyroid Gland
The Parathyroid Glands

3. Overview of the Endocrine System
The endocrine system consists of collections of cells located in tissues scattered throughout the body that produce substances released into the blood (hormones) to ultimately affect the activity and metabolism of target cells.
The endocrine system consists of collections of cells located in tissues scattered throughout the body that produce substances released into the blood (hormones) to ultimately affect the activity and metabolism of target cells.
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

4. Endocrine System Endocrine glands are ductless
Effects of hormones are INTRAcellular
Exocrine glands have ducts
Effects are EXTRAcellular
Figure from: Hole’s Human A&P, 12th edition, 2010

5. Endocrine Glands Endocrine glands release hormones
hormones travel throughout body in blood to targets
targets must have receptors to respond
Paracrine secretions
act locally
do not travel through blood
Autocrine secretions
affect only the secreting cell
Hormones regulate metabolic processes and change activity of cells
- Rates of biochemical reactions - Water/electrolyte balance - Blood pressure - Reproduction, development, and growth
Examples of paracrine factors: histamine and NO (smooth muscle of blood vessels), somatostatin in pancreas (inhib. Insulin/glucagon secrn), eicosanoids.

6. Comparison of Nervous and Endocrine Systems
Figure from: Hole’s Human A&P, 12th edition, 2010
Neurons release neurotransmitters into a synapse, affecting postsynaptic cells
Glands release hormones into the bloodstream
Only target of hormone responds

7. Control of Hormone Secretion
Ca2+
Blood plasma
Ca2+
Endocrine organ #1
Ca2+
Ca2+
Ca2+
Ca2+
2) Humoral control
3) Hormonal control
(Hormone)
Ca2+
1) Neural control
Endocrine organ
Endocrine organ #2
Endocrine organ
Hormone secretion

8. Classification of Hormones
Amino acids
Amino Acid Derivatives
Peptides
Proteins, glycoproteins
Hormones
Steroids (cholesterol-derived)
Lipid Derived
Hormones can be broadly grouped into steroid hormones, which are lipid-soluble and exert their actions by binding to intranuclear receptors, and amino acid-derived hormones, which are water soluble and exert their actions via second messengers.
Eicosanoids (cell membranes) (locally acting)

9. Eicosanoid Synthesis
Eicosanoids are important paracrine factors that mediate many processes in the body, including:
Inflammation - blood vessel constriction - blood clotting - smooth muscle contraction and relaxation

10. Types of Hormones
Figure from: Hole’s Human A&P, 12th edition, 2010

11. Steroid Hormones Composed of rings of C and H
Steroid hormones are hydrophobic, i.e., lipid soluble
What does this mean for
- Blood (plasma) solubility?
- Cell membrane solubility?
Cholesterol - Cyclopentanoperhydrophenanthrene

12. Actions of Steroid Hormones
hormone crosses membranes
Figure from: Hole’s Human A&P, 12th edition, 2010
hormone combines with receptor in nucleus or cytoplasm
synthesis of mRNA activated
mRNA enters cytoplasm to direct synthesis of protein, e.g., aldosterone->Na/K Pump
Example of this: aldosterone. Binding of aldosterone to nuclear receptors triggers the cell to make Na-K ATPase pump, the sodium pump that exchanges K+ for Na+
(Thyroid hormone has a similar mechanism of action, even though it is a tyrosine derivative)
Magnitude of cellular response proportional to the number of hormone-receptor complexes formed

13. Amino Acid-Derived Hormones
Figure from: Hole’s Human A&P, 12th edition, 2010
Water soluble (hydrophilic)
What does this imply about their solubility in blood and the cell membrane?

14. Actions of Amino Acid-Derived Hormones
Figure from: Hole’s Human A&P, 12th edition, 2010
hormone (first messenger) binds to receptor on cell membrane
adenylate cyclase activated
ATP converted to cAMP
cAMP (second messenger) promotes a series of reactions leading to cellular changes
Example: TSH stimulates the synthesis of the thyroid hormone, thyroxine. Binding of GH activates anabolic reactions in which aa are made into proteins.
Magnitude of response is not directly proportional to the number of hormone-receptor complexes – it’s amplified

15. Target Cell Activation by Hormones
Target cells must have specific receptors to be activated by hormones
Target cell activation depends upon
Blood levels of the hormone
Rate of release from producing organ
Rate of degradation (target cells, kidney, liver)
Half-life
Relative numbers of receptors for the hormone
Cellular receptors can be up- or down-regulated
Affinity (strength) of binding of the hormone to its receptor

16. Negative Feedback for Hormone Regulation
Figure from: Hole’s Human A&P, 12th edition, 2010
Recall that homeostasis is the maintenance of STABLE (not constant) internal conditions

17. Control of Hormonal Secretions
Figure from: Hole’s Human A&P, 12th edition, 2010
primarily controlled by negative feedback mechanism
Humoral example: Ca blood levels and PTH, glucose levels and insulin/glucagon secretion
Neural example: SNS stimulation of adrenal medulla, dopaminergic control of prolactin release by hypothalamus, milk letdown, sympath control of endocrine pancreas
Hormonal example: TSH, ACTH, somatostatin inhibition of growth hormone release.
Humoral
Hormonal
Neural
Control mechanisms for hormone release

18. Major Endocrine Glands
Figure from: Hole’s Human A&P, 12th edition, 2010

19. Pituitary Gland (Hypophysis)
Two distinct portions
anterior pituitary (adenohypophysis)
posterior pituitary (neurohypophysis)
Figure from: Hole’s Human A&P, 12th edition, 2010

20. Overview of the Pituitary Hormones
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
All anterior and posterior pituitary hormones bind to membrane receptors and use 2nd messengers (cAMP)
SeT GAP
The pituitary gland consists of two anatomically and functionally distinct portions. The anterior pituitary (adenohypophysis) is a glandular structure that produces and releases hormones in response to releasing hormones from the hypothalamus to which it is connected by a hypophyseal portal system. The posterior pituitary (neurohypophysis) stores and releases hormones produced in the hypothalamus after neural stimulation.

21. Pituitary Gland Control
Figure from: Hole’s Human A&P, 12th edition, 2010
Hypothalamic releasing hormones stimulate cells of anterior pituitary to release their hormones
Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release its hormones
Note the hypophyseal portal system (two capillaries in series)

22. Hormones of the Anterior Pituitary (SeT GAP)
Figure from: Hole’s Human A&P, 12th edition, 2010
(an ‘axis’)
Tropic hormones (in black  ) control the activity of other endocrine glands
All anterior pituitary hormones use second messengers

23. Anterior Pituitary Hormones
Pro-opiomelanocortin (POMC) has also been isolated from the anterior pituitary
A prohormone that must be split enzymatically in order to become active
POMC is the source of several other hormones
ACTH
Natural opiates (enkephalin, -endorphin)
Melanocyte-stimulating hormone (MSH)

24. Anterior Pituitary Hormones - GH
Growth Hormone (GH)
main target is skeletal muscle, bone, and cartilage
stimulates increase in size and metabolic rate of body cells
anabolic (tissue building) and diabetogenic ( [glucose])
Circadian (24-hour) pattern of secretion - highest during sleep
action via insulin-like growth factors (somatomedins)
enhances movement of amino acids through membranes
promotes lipolysis and glycogenolysis (diabetogenic effect)
promotes growth of long bones
secretion inhibited by somatostatin (GHIH)
somatotrope secretion stimulated by growth hormone-releasing hormone (GHRH)

25. Anterior Pituitary Hormones - PRL
Prolactin (PRL)
stimulates milk production by the breasts (rises at end of pregnancy; infant suckling after birth)
amplifies effect of LH in males ( sens. of interstitial cells)
secretion inhibited by hypothalamic PIH (dopamine)
secretion stimulated by PRF (serotonin?)
produced by lactotropes (mammotropes)
brief rise in PRL levels just before menstrual period partially accounts for breast swelling and tenderness

26. Anterior Pituitary Hormones – TSH/ACTH
Thyroid Stimulating Hormone (TSH)
controls secretions of hormones from the thyroid gland
release controlled by thyrotropin-releasing hormone (TRH) from the hypothalamus
produced by thyrotropes
Adrenocorticotropic Hormone (ACTH)
controls secretions of some hormones of adrenal cortex
release controlled by corticotropin-releasing hormone (CRH) from the hypothalamus
produced by corticotropes
What term would describe these two hormones that cause the secretion of other hormones in distant endocrine tissues?
- Tropic hormones -

27. Anterior Pituitary Hormones – FSH/LH
- Tropic hormones -
Follicle-Stimulating Hormone (FSH)
stimulates gamete production in males and females
controlled by gonadotropin-releasing hormone (GnRH)
stimulates follicular cells to secrete estrogen
Luteinizing Hormone (LH)
promotes secretions of sex hormones in both sexes
controlled by gonadotropin-releasing hormone (GnRH)
stimulates release of egg from ovaries in females promotes growth of long bones
known as Interstitial Cell Stimulating Hormone in males
FSH and LH are gonadotropins produced by gonadotropes

28. Posterior Pituitary Hormones – ADH/OT
Antidiuretic Hormone (ADH; vasopressin or AVP)
causes kidneys to reduce water excretion
in high concentration, raises blood pressure
controlled by hypothalamus in response to changes in blood water concentration (osmoreceptors) and blood volume
inhibited by alcohol, diuretics
Oxytocin (OT) – smooth muscle contraction
stimulates uterine contractions
stimulates lactating mammary glands to eject milk
controlled by hypothalamus in response to stretch in uterine and vaginal walls and stimulation of breasts
thought also to play a role in sexual arousal, orgasm, sexual satisfaction, and promotion of “cuddling behavior”
Both hormones use IP3-calcium second messenger

29. Thyroid Gland
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

30. Thyroid Gland Follicular cells produce thyroglobulin (TG)
After being attached to iodine, TG is stored in colloid in the follicles
I-bound TG is the source of thyroid hormones, T3 (3 I-) and T4 (4 I-)
Parafollicular cells, or ‘C’, cells, of the thyroid gland produce calcitonin
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

31. Thyroid Hormones Thyroxine (T4) and Triiodothyronine (T3)
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Thyroxine (T4) and Triiodothyronine (T3)
increases BMR and rate of energy release from CHO (calorigenic effect)
↑ rate of protein synthesis
accelerates growth; critical for skeletal/nervous system
important for reproductive function
release controlled by TSH (from anterior pituitary); highest before sleep and at night

32. Thyroid Gland Disorders
General Hyperthyroidism
high metabolic rate
hyperactivity
weight loss
protruding eyes
Congenital hypothyroidism (Older terminology - Cretinism)
hypothyroidism in infants
leads to small stature and mental retardation

33. Thyroid Gland Disorders
Myxedema
adult hypothyroidism
low metabolic rate
sluggishness
Simple (Endemic) Goiter
deficiency of iodine
leads to deficiency of thyroid hormones
thyroid gland enlarges
Grave’s disease
overstimulation of gland by antibodies that mimic TSH
hyperthyroidism

34. Calcitonin Calcitonin3 1
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 2
Calcitonin
lowers blood calcium and phosphate ion concentrations by inhibiting release of calcium and phosphate from bones
increases rate at which calcium and phosphate are deposited in bones
most important in children; weak hypocalcemic agent in adults

35. Parathyroid Glands PTH (parathormone, parathyroid hormone)
Figure from: Hole’s Human A&P, 12th edition, 2010
PTH (parathormone, parathyroid hormone)
increases blood calcium levels
stimulates bone resorption by osteoclasts
stimulates kidneys to retain calcium and excrete phosphate
promotes calcium absorption into intestine

36. Parathyroid Hormone 1 3
Parathyroid cells driven by a G-protein Ca2+ sensor protein. The sensor is activated by high Ca2+ levels and causes a cascade that increases PTH degradation and decreases PTH release. Low Ca2+ levels allow increased PTH release. 2
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
** Calcium ion homeostasis is maintained by a negative feedback system involving a pair of hormones with opposite effects, PTH and calcitonin

37. Parathyroid Glands
PTH promotes Ca2+ absorption in the intestine (via vitamin D) and Ca2+ reabsorption by the kidney
Figure from: Hole’s Human A&P, 12th edition, 2010

38. Overview of Calcium Homeostasis
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

39. Review The endocrine system consists of…
Tissues scattered throughout the body that secrete…
Hormones, which are chemical messengers,
Into the blood to circulate throughout the body
And affect metabolism/activity of target cells
A major control system of the body
Regulates many body functions
Rates of reactions
Transport of substances
Water and electrolyte balance
Blood pressure
Reproduction, development, and growth

40. Review Hormones can be divided chemically into Amino acid derivatives
Peptides, proteins, glycoproteins, amines
Water soluble (cannot cross cell membranes)
Use membrane-based receptors
Response can be amplified by intracellular cascades
Use second messengers (cAMP, cGMP, DAG, IP3)
Examples: norepinephrine, insulin, ADH, TSH
Steroid hormones
Composed of rings of C and H
Lipid soluble (can cross cell membranes)
Response is proportional to number of intracellular hormone-receptor complexes
Examples: Sex hormones, aldosterone, cortisol

41. Review Hormone release is controlled by
Humoral factors, e.g., blood [Ca2+], [glucose]
Neural mechanisms, e.g., SNS stimulation of adrenal medulla
Hormonal mechanisms, e.g., hypothalamus-pituitary
Control of hormone secretion is mostly accomplished by negative feedback

42. Review The pituitary gland is a major site of hormone production
Anterior (adenohypophysis)
Hormone secreting cells
Release controlled by hypothalamic releasing hormones
ACTH, GH, LH/FSH, Prolactin, TSH
Posterior (neurohypophysis)
Storage area for hormones produced in the hypothalamus
Release controlled by neural activity
ADH and OT

43. Hormone Summary Table I – Pituitary Hormones
Tissue
Name
Origin
Destination
Action on Target Tissue
Control of Release1
FOLLICLE STIMULATING HORMONE (FSH)
anterior pituitary
males: semiiferous tubules of testes;
females: ovarian follicle
males: sperm production
females: follicle/ovum maturation
Gonadotropin Releasing Hormone (GnRH)
LUETINIZING HORMONE (LH)
In males: interstitial cells in testes;
in females: mature ovarian follicle
males: testosterone secretion
females: ovulation
THYROID STIMULATING HORMONE (TSH)
thyroid
secrete hormones
Thyrotropin Releasing Hormone (TRH)
GROWTH HORMONE (GH)
bone, muscle, fat
growth of tissues
Growth Hormone Rleasing Hormone (GHRH)
ADRENOCORTICO-TROPIC HORMONE (ACTH)
adrenal cortex
secrete adrenal hormones
Corticotropin Releasing Hormone (CRH)
PROLACTIN (PRL)
mammary glands
produce milk
Prolactin Releasing Hormone (PRH)
ANTI-DIURETIC HORMONE (ADH)
(VASOPRESSIN)
posterior pituitary
distal convoluted tubule (DCT)
reabsorption of water; increases blood pressure
increase in osmolarity of plasma or a decrease in blood volume
OXYTOCIN (OT)
uterine smooth muscle; breast
contraction during labor; milk letdown
Stretching of uterus; infant suckling
Se(x) T G A P

44. Review
HORMONE
SECRETED BY WHAT GLAND?
TARGET(S)?
EFFECT(S) AT TARGET SITE
Triiodothyronine (T3) & Thyroxine (T4)
Thyroid (follicular cells)
all cells
increases rate of metabolism
Calcitonin
Thyroid (C cells)
Distal convoluted tubules and osteoblasts
secretion of Ca++ into urine, bone formation (de-creases blood Ca++)
Parathyroid Hormone (PTH)
Parathyroids
Proximal kidney tubules, osteoclasts, intestine
reabsorption of Ca++ into blood, bone resorption, dietary Ca ++ absorption
(increases blood Ca++)
Remember that PTH and calcitonin have opposing effects in regulating blood calcium levels (they are antagonists)