chapter 18 part 2 thyroid gland –synthesis and function of thyroid hormone calcitonin and calcium...

Chapter 18 Part 2• Thyroid Gland

– Synthesis and function of Thyroid hormone Calcitonin and Calcium regulation

• Parathyroid Gland– PTH and Calcium regulation

• Adrenal Gland– The corticosteroids

• Pancreas– Regulation of blood glucose

Thyroid Gland

• Covers anterior surface of trachea

• 2 lobes with isthmusTrachea

Hyoid Bone

Isthmus

lobe of thyroidlobe of thyroid

Thyroid gland • Tissue consists of follicles • Follicles are hollow spheres

lined with epithelial cells (follicle cells)

• Follicular cells take up Iodine from circulation and produce thryoglobulin (the precursor to thyroid hormone)

• Thyroglobulin is stored in the colloid of follicle

• C cells produce calcitonin (CT)

Thyroid Gland

Here thyroglobulin, a glycoprotein, is stained hot pink

An elusive C-cell is indicated

Synthesis of thyroid hormone

Synthesis of thyroid hormone

• A funky, multistep process• Iodine selectively pumped into the membrane of

follicular cells• Iodine bound to tyrosine molecules, forming

thyroid hormone, incorporated into thyroglobulin• Thyroglobulin is stored in follicle• Upon TSH stimulation, thyroglobulin is

endocytosed back into follicle cell, diffuses across cell, and released into bloodstream

T4 versus T3

• What is the difference?

• The thyroid releases 90% T4, 10% T3

• T3 is the active form!

Functions of Thyroid Hormone

• Actively transported into all cells of body• Binds mitochondria, increases rate of mitochondrial

ATP production• Binds nuclear receptors and increases transcription

of Na+/K+ ATPase• Also activates genes that code for enzymes involved

in glycolysis and ATP production• PUNCHLINE: Thyroid hormone increases basal

metabolic rate

Thyroid Hormone Regulation

Misregulation and Goiters• TSH causes

thyroid hormone release AND growth of thyroid tissue

C cells and Calcitonin

• C cells respond directly to high levels of Ca2+ in body fluids

• Release Calcitonin (CT), works to reduce Ca2+ concentration in body fluids

• How??

Calcitonin and Ca2+ regulation

• Inhibition of osteoclasts (the bone breaker-downer cells)

• Stimulation of Ca2+ excretion at kidneys

CT

osteoclast

Parathyroid Glands• Located on the posterior

aspect of the thyroid gland• Chief cells produce and

release parathyroid hormone (PTH) directly in response to low circulating Ca2+ levels

• PTH works to increase Ca2+ levels

Parathyroid Glands• Stimulates osteoclasts• Inhibit osteoblasts

(decreases rate of Ca2+ deposition)

• Increases Ca2+ resorption at kidnes

• Stimulates formation of calcitriol at kidneys (works at gut)

PTHChomp, chomp!

osteoclast

PTH and Calcitonin regulate Ca2+ levels

Adrenal Gland

•The cortex has three cellular regions (zones), each that makes specific hormones

–Zona glomerulosa (outermost)–Zona fasciculata (middle)–Zona reticularis (innermost)

cortex

medulla

Adrenal Gland

250uM

medulla

Adrenal Cortex

• Endocrine tissue that produces a variety of corticosteroids (general term for steroids from the cortex)

• All affect gene transcription• This collection of steroids are vital to life• The cortex has three cellular regions (zones), each

that makes specific hormones– Zona glomerulosa: Mineralocorticoids– Zona fasciculata: Glucocorticoids– Zona reticularis: Androgens

Adrenal CortexZona glomerulosa

-Mineralocorticoids• Aldosterone, the “Na+ saver”• Its release is triggered by a drop in blood

Na+, blood volume or blood pressure• Aldosterone works at: kidneys, sweat glands,

salivary glands and pancreas to decrease Na+ secretion/release

• Effect: water follows Na+, so water is saved, as well

Adrenal Cortex

• Zona fasciculata– Glucocorticoids

• When stimulated by ACTH, cortisol and corticosterone secreted (and cortisone is converted from cortisol by the liver)

• Glucocorticoids exhibit negative feedback at both the hypothalamus and anterior pituitary

Effects of Glucocorticoids

• Accelerate rates of glucose synthesis and glycogen formation, especially at liver

• Adipose breaks down TG into Fas

• Anti-inflammatory effects– Inhibit WBC and other immune system

fuction– Slow migration of phagocytic cells into

injury site, and decrease activity– Negative effects on wound healing

Adrenal cortex

• Zona Reticularis– Produces androgens

Adrenal Medulla

• What is the composition of this part of the gland?

• What triggers the release?

• What hormones are produced?

Adrenal MedullaSympathetic division Parasympathetic division

Effects of Adrenal Medulla Stimulation

• @ skeletal muscles: mobilize glycogen reserves, increase beakdown of glucose into ATP

• @ adipose tissue: stored fats are broken down, fatty acids into circulation

• @ liver: glycogen breakdown (the brain needs glucose!)

• @ heart, 1 receptors stimulated, increase in cardiac force and rate

Pancreas

• A unique gland with both exocrine and endocrine functions– Exocrine: produces enzymes for digestion– Endocrine: produces hormones for blood

glucose regulation

Endocrine Islets in a sea of exocrine cells (acinar cells)

A single islet containing and cells

Histology of the Pancreas

Regulation of Blood Glucose

cells release glucagon

cells release insulin

Nutshell version:

Normal blood glucose levels = 70-110 mg/dL --When blood glucose is low, glucagon stimulates glycogen breakdown and glucose release from liver

--When glucose levels are elevated, insulin encourages the uptake use, and storage of glucose

Regulation of blood glucose

gluconeogenesis

One example in detail

• How does insulin actually increase glucose uptake by cells?

• This process is not totally understood and is an area of intensive research.

• Glucose transporter discovered in mid 1980’s

http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html

http://research.imb.uq.edu.au/~l.rathbone/glut4/

Diabetes

• 17 million Americans have Type 2 (adult-onset) diabetes, a disorder in which cells lose their ability to absorb glucose from the blood stream.

• This is different from Type 1 (juvenile onset) diabetes, in which the immune system attacks insulin-producing, cells.

What tissues, organs suffer in diabetic state? Why?