Histology of Endocrine Organs (Brauer)

Question 1

What is difference between the endocrine and nervous system?

Answer 1

• Nervous:
  
  • Rapid communication
  • Short lived effects
• Endocrine:
  
  • Slower communication via release of hormones into blood and binding on receptor cells
  • Longer lasting effects

Question 2

What are the stimuli that control hormonal release?

Answer 2

• Humoral
• Neuronal
• Hormonal

Question 3

What is humoral stimuli?

Answer 3

Release of hormones are controlled by levels of ions and nutrients in blood/body fluids

Ex: PTH stimulated by low Ca²⁺ levels

Question 4

What is neuronal stimuli?

Answer 4

Release of hormones stimulated by nerve signals

Ex: Epinephrine is relased from adrenal gland signaling via sympathetic nerve fibers

Question 5

What is hormonal stimuli?

Answer 5

Hormones secreted into the blood by another endocrine tissue

Ex: TSH from pituitary gland stimulates TH release in the thyroid

Question 6

How are endocrine glands organized?

Answer 6

Epithelioid cells arranged as follicles which lack free surfaces (does not open to lumen). They are well vascularized with fenestrated endothelium.

Question 7

What are the direct targets of hypothalamic hormones?

Answer 7

• Anterior pituitary gland (releasing and inhibiting factors)
• Kindey and uterus (ADH & Oxytocin stored in posterior pituitary)
• Adrenal medulla (sympathetic innervation)

Question 8

What are the indirect targets of hypothalamic hormones and how are the stimulated?

Answer 8

Indirectly influenced by stimulating secretion of hormones by the anterior pituitary

TSH –> ​Thyroid gland

ACTH –> Adrenal cortex

Prolactin –> Mammary gland

FSH/LH –> Gonads

GH & MSH –> Bone & other organs

Question 9

What are the embryoligcal origins of the anterior and posterior pituitary gland?

Answer 9

• Anterior Pituitary: Surface Ectoderm
  
  • From Rathke’s Pouch
• Posterior Pituitary: Neuroectoderm
  
  • From diencephalon

Question 10

What kind of cell types compose most of the anterior pituitary gland?

Answer 10

Glandular epithelial cells controlled by neurohormones released from hypothalamus

Question 11

What composes most of the posterior pituitary gland?

Answer 11

Axons from hypothalamus and support cells

Looks like nerve tissue

Question 12

Identify the various components of the pituitary gland

Answer 12

• Pars Distalis
• Pars Nervosa
• Pars Tuberalis
• Pars Intermedia
• Cyst Intemedia: remnant of lumen of Rathke’s pouch

Question 13

What are some major cell types in the Pars Distalis (Anterior pituitary)?

Are they acidophilic or basophilic?

Answer 13

Acidophilic:

• Somatotropic cells
• Mammotropic cells

Basophilic:

• Thyrotropic cells
• Corticotropic cells
• Gonadotropic cells

Chromophobes - unknown function

Sinusoidal (fenestrated) capillaries

Question 14

What do somatotroph cells release?

How do they stain?

Answer 14

• Secrete Growth Hormone (GH) in response to GHRH
• Acidophilic (lighter)

Question 15

What do mammotroph cells release?

How do they stain?

Answer 15

• Secrete prolactin to stimulate milk production
• Acidophilic (stain lighter)

Question 16

What do corticotroph cells release?

How do they stain?

Answer 16

• Secrete ACTH: stimulates adrenal cortex to secrete stress related hormones and mediate metabolism
• Basophilic (stains lighter)

Question 17

What do thyrotroph cells release?

How do they stain?

Answer 17

• Secrete TSH
• Basophilic (stain darker)

Question 18

What do gonadotropic cells release?

How do they stain?

Answer 18

• Secrete FSH and LH
• Basophilic (stain darker)

Question 19

What is the Pars Nervosa

Answer 19

Posterior part of the Pituitary gland. Continues with the median emince of the hypothalmus via the infundibular stalk. It does not manufacture hormones, rather it stores and releases them from axon terminals

Question 20

What does the pars nervosa consist of?

Answer 20

• Unmyelinated axons from hypothalamus
• Herring bodies: axonal nerve terminals that store ADH and oxytocin
• Pituicytes: glia like
• Fenestrated capillaries

Question 21

How does blood supply to the hypothalamo-hypophyseal portal system work?

Answer 21

1. Primary Capillary Plexus: Hormones released from hypothalamus to anterior pituitary
2. Hormones travel through portal veins in anterior pituitary
3. Secondary Capillary Plexus: hormones from anterior pituitary gland enter general circulation to reach targers

Question 22

How does the hypothalmo-hypophyseal tract work in the posterior pituitary gland?

Answer 22

1. Hypothalamus synthesize ADH and oxytocin
2. ADH and oxytocin are transported to posterior pituitary for storage
3. ADH and oxytocin are released via hypothalamic signals

Question 23

Where is the pineal gland located?

What does it consist of?

Answer 23

Outpocketing of diencephalon’s roof of the third ventricle

Consists of

• Pinealocytes: secretes melatonin
• Neuroglia
• Calcified granular material

Question 24

What is the function of the pineal gland?

Answer 24

• Regulates growth, development, and circadian rhythms
• Snythesizes serotonin and melatonin

Question 25

What are the histological characteristics of the thyroid gland? What is unique about the thyroid?

Answer 25

* Contains **follicles** with a layer of follicular cells (simple cuboidal/simple columnar) surrounding **colloid** fluid * Colloid contains thyroglobulin (storage form of T3 and T4) * Only gland to store hormones outside of the cell

Question 26

How are thyroid hormones synthesized and releasd?

Answer 26

1. Thyroglobulin are synthesized in rER, glycosylated in Golgi and stored in lumen (colloid fluid) 2. Thyroglobulin is iodinated at the apical surface forming T3 and T4 3. TSH stimulates internalization of thyroglobilun via endocytosis, freeing T3 and T4 and releasing them from basal surface into the blood

Question 27

**Parafollicular C Cell** Where is it located? What is its function?

Answer 27

Located near follicles in thyroid gland (periphary). Function is to secrete calcitonin when blood levels of calcium are high ***Calcitionin tones down calcium***

Question 28

How does calcitonin lower circultaing calcium levels

Answer 28

1. Stimulates excretion of Ca²⁺ by kidneys 2. Decreases Ca²⁺ releasing activity of osteoclasts 3. Increases osteogenesis by osteoblasts

Question 29

What is Grave's Disease and its sypmtoms? How does it occur?

Answer 29

* Abnormal antibodies stimulate TSH receptors, _increasing secretion of T3 and T4 from thyroid_ * Symptoms: * Elevated metabolism * Sweating * Rapid HR * Weight Loss * Eyeballs may protrude * More common in women

Question 30

How does ​hypothyroidism occur? What is its symptoms?

Answer 30

* Insufficient T3 and T4 production most likely due to an autoimmune disease * Symptoms: * Low metabolic rate * Weight gain * Lethargy * Chilliness * Edema * Mental sluggishness

Question 31

What can cause a goiter?

Answer 31

* Thyroid enlargement due to **iodine** deficiency * Follicular cells keep making thyroglobulin but cannot iodinize it to make T3 or T4

Question 32

**Parathyroid Glands** Where are they located? What cell types are present? What hormones do they release?

Answer 32

* Found on posterior surface of thyroid * Function: Release hormones to regulate calcium and phosphate levels * Chief cells: Release **Parathyroid hormones (PTH)** when blood conc. of calcium falls below normal range. * Oxyphil cells: function unknown

Question 33

How does PTH regulate calcium levels?

Answer 33

* If calcium levels low (\<9.5 mg/dL), parathyroid releases PTH into bloodstream * Stimulates osteoclasts to resorb bone and release Ca²⁺ stores * Increase calcium retention by the kidneys * Stimulates kidney to convert inactive form of Vitamin D to Calcitriol * Calcitriol increases Ca²⁺ absorption by intestines * As calcium levels increase, PTH is inhibited

Question 34

What are the three layers of the adrenal cortex and what are their functions?

Answer 34

* **Zona Glomerulosa (mineralcorticoids):** Influence Na+ and K+ levels * _Aldosterone:_ secreted in response to low BP/BV * **Zona Fasciculata (glucocorticoids):** Influences glucose metabolism and immune system. Controlled by ACTH * _Cortisol:_ secreted to deal with stress and mediate glucose. Also negative feedback to immune system * **Zona Reticularis:** Influence secondary sex characteristics * Androgens released

Question 35

Label the following components of the adrenal gland. What hormones are secreted by 1-4?

Answer 35

1. Zona glomerulosa: aldosterone 2. Zona fasciculata: Cortisol 3. Zona Reticularis: Androgens 4. Medulla: NE and EPI 5. Cortex 6. Medulla

Question 36

What is the Adrenal Medulla

Answer 36

* Inner core of adrenal gland that consists of chromaffin cells * Stiumlated by presynaptic sympathetic to secrete epinephrine and norepinephrine to prepare body for an emergency or flight or fight situation

Question 37

**Addison's Disease** What causes it? What are its symptoms?

Answer 37

* _Hyposecretion_ of glucocorticoids and mineralcorticoids * Blood glucose and sodium levels drop * Causes: autoimmune disease or inherited metabolic disease leading to enzyme deficiencies * Symptoms * Hypotension * severe dehyration * Fatigue * Loss of appetite

Question 38

**Cushing's Syndrome** What causes it? What are its symptoms?

Answer 38

* _Hypersecretion_ of glucocorticoids * Causes: * ACTH secreting tumor in pituitary gland * Tumor in adrenal cortex * Symptoms: * High serum glucose levels * Protein loss in muscle * Muscle weakness * Lethargy * Swollen Face * Fat redistribution * Depression of immune responses

Question 39

How is the pancrease organized?

Answer 39

**Exocrine Portion:** majority of pancreas * Aids in digestion * Organized as _pancreatic acini_ **Endocrine Portion:** * Organized as pancreatic islets or islets of Langerhans * Scattered among exocrine cells

Question 40

What cells are found in the endocrine pancreas?

Answer 40

* **Alpha cells:** secrete _glucagon_ when glucose levels are low * Releases glucose from liver glycogen stores * **Beta cells:** _insulin_ when glucose levels are high * Promotes glycogen storage and entry of glucose into cells * **Delta cells:** _somatostatin_ to slow the release of insulin and glucagon * Stimulated by high levels of nutrients in the blood * **F cells:** _pancreatic polypeptide_ that inhibits release of somatostatin

Question 41

Explain the pancreatic blood supply

Answer 41

Dual blood supply by Acinar vascular system and Insuloacinar portal system