BIO 202: Lab Exercise 1.1-1.3 - Endocrine system anatomy, histology, and negative feedback loop

What is the endocrine’s primary means of travel and 1 of the only 2 liquid tissues in the body (other than cerebrospinal fluid/CSF)

Blood (it’s considered a connective tissue)

What are the 2 main components of blood

Plasma: the liquid portion (55%)
Formed elements: cells and fragments (45%)

What is the endocrine system

A diverse group of ductless glands that play a major role in maintaining homeostasis of multiple physiological variables

What are exocrine glands and examples

Glands that rely on ducts to secrete their glands.
For example: sweat, salivary, lacrimal, digestive, and mammary glands

What other system does the endocrine system work closely with to maintain homeostasis of multiple physiological variables and what do they do together

Nervous system - They both provide a mean for regulating other organ systems/tissues and maintaining homeostasis (maintaining internal communication and coordination)

How does the nervous system function

Via action potentials (nerve impulses) and releases neurotransmitters that directly affect target cells. Effects are immediate but short in duration

How does the endocrine system function

Via secretion of hormones (chemicals released into bloodstream) that typically act on distant targets. Effects are not immediate but are longer-lasting than nervous system

What do hormones regulate

The processes of other cells, including production of enzymes/other hormones, changing metabolic rate of a cell, and altering permeability of plasma membrane.
Hormones are the “middle managers” that communicate messages from bosses (endocrine glands) to workers (other cells)

What endocrine glands secrete their hormones as secondary function

Heart (atrial natriuretic peptide), adipose tissue (leptin), kidneys (erythropoietin), and stomach (gastrin)

What type of system is the nervous and endocrine system referred to as

Nervous system is referred to as fast response system and has specific/localized targets
Endocrine system is referred to as slow response system and take hours/days/weeks or longer to produce noticeable changes

What are the 10 endocrine organs that have secretion as a primary function

Hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pancreas, ovaries, testes

Where is the hypothalamus located and what is it known as

In inferior part of diencephalon and is known as neuroendocrine organ.

What does the hypothalamus labeled as and what does it works with

Labeled as the endocrine system’s chief executive officer (CEO) and works closely with pituitary gland that is attached by infundibulum

What hormones does the hypothalamus secrete and interact with and do (remember: they are still produced by hypothalamus)

• Interacts with the anterior pituitary: inhibiting and releasing hormones - inhibit and stimulate secretion from anterior pituitary

• Interacts with posterior pituitary: oxytocin - triggers uterine contraction and milk ejection from mammary glands (oxy:sharp, tocin:childbirth) and antidiuretic hormone (ADH) - causes water retention in kidneys and assist with blood pressure control (anti:against, diuretic:urine)

How does the hypothalamus communicate with the anterior pituitary gland

By specialized set of blood vessels called hypothalamic - hypophyseal portal system (HHPS)

What is the pathway of the hypothalamic - hypophyseal portal system

Inhibiting and releasing hormones are synthesized by hypothalamic neurons → they enter capillaries in hypothalamus → they travel through small veins in infundibulum → they enter a second capillary bed in anterior pituitary → they exit blood and interact with anterior pituitary cells

What 2 regions is the pituitary gland made up of, its alternative name, and what is it composed of

Anterior pituitary gland or adenohypophysis: composed of glandular epithelium
Posterior pituitary or neurohypophysis: composed of nervous tissue

What type of hormones does the anterior pituitary gland secrete in the pituitary gland that stimulate other endocrine and exocrine glands in the body?

Tropic hormones that influences the functions of other endocrine and exocrine glands (tropic hormones act on endocrine glands to release whereas non-tropic hormones act directly on tissues/organs)

What hormones does the anterior pituitary gland secrete in the pituitary gland and their functions

• Follicle-stimulating hormone (FSH): stimulates follicles in ovary & sustentacular cells in testes (reproductive hormone)

• Luteinizing hormone (LH): stimulates oocytes in ovary & interstitial cells in testes (reproductive hormone)

• Adrenocorticotropic hormone (ACTH): stimulates secretion from adrenal cortex

• Thyroid-stimulating hormone (TSH): stimulates growth & secretion from thyroid gland

• Prolactin: stimulates milk production from mammary glands

• Growth hormone (GH): increase rate of cell division and protein synthesis - has both tropic and non-tropic effects

• Mnemonic: FLAT-PG

What hormones does the posterior pituitary gland produce in the pituitary gland

It does not produce hormones, it functions as a storage to store oxytocin and antidiuretic hormone produced by hypothalamus

Where is the pineal gland located and what type of endocrine organ is it

In posterior and superior diencephalon. It is a neuroendocrine organ

What hormones does the pineal gland secrete and in response to what? What does the hormone act on?

Secretes melatonin in response to decreased light levels. It acts on the reticular formation part of the brainstem to trigger sleep

Where is the thyroid gland located and what does it consist of and connected by?

In anterior-inferior neck, superficial to larynx/voicebox. It consist of right and left lobes that are connected by a thin band of tissues called isthmus

What is the thyroid gland composed of and its parts?

Hollow spheres called thyroid follicles that are lined with simple cuboidal follicle cells. The thyroid follicles encapsulates colloid (gelatinous, iodine-rich substance)

What does follicle cells respond to and how in the thyroid gland?

Responds to TSH (thyroid-stimulating hormone) from anterior pituitary by secreting a chemical into the colloid that reacts with iodine to produce the 2 hormones

What hormones does the thyroid gland produce and their components?

Thyroxine (T4): 4 iodine molecules
and triiodothyronine (T3): 3 iodine molecules - most active and it increases metabolic rate & protein synthesis, and regulates heart rate and blood pressure.
*About 10x as much T4 is produced as T3 so body converts T4 to T3 when levels drop

What are in between the follicle cels in the thyroid gland and what does it produce?

Parafollicular cells that produce calcitonin

What is the antagonist of parathyroid hormone and its function?

Calcitonin: used to lower blood calcium levels by triggering osteoblast activity and bone deposition.

Where are the parathyroid glands located and what hormones does it secrete

Posterior side of the thyroid gland
Secretes parathyroid hormone (PTH)

What is the antagonist of calcitonin and its function?

Parathyroid hormone (PTH): the main hormone that maintains calcium ion homeostasis. It increases blood calcium levels by triggering osteoclast activity and resorption/losing of bone tissue. It increases calcium ion absorption from intestines and increases calcium ion reabsorption from kidneys

Where is the thymus gland located

Sits in the superior mediastinum

Describe the thymus gland and its hormones.

It’s large and activated in infancy and early childhood, during which it secretes thymosin and thymopoietin → which stimulate the development of T lymphocytes within thymus gland.
In adults, it turns into fat and other connect tissue

Where is the adrenal gland located

Sit atop the superior pole of each kidney (ad: next to, renal: kidney)

What are the 2 structures the adrenal gland is composed of?

Outer adrenal cortex and inner adrenal medulla

What are adrenal glands surrounded by?

Thin layer of connective tissue called adrenal capsule

What is the adrenal cortex, what does it consist of, and what type of hormones does it secrete and derived from?

The superficial region of the adrenal gland consisting of glandular tissue. It secretes steroid hormones derived from cholesterol in response to stimulation by adrenocorticotropic hormone

What are the hormones the adrenal cortex secrete and an example

• Zona-GFR:

• Zona glomerulosa: outermost zona of adrenal cortex → secretes mineralocorticoids & an example is aldosterone which regulates fluid, electrolyte, & acid-base balance

• Zona fasciculata: middle zone of adrenal cortex → secretes glucocorticoids & an example is cotisol which regulates stress response, blood glucose, fluid homeostasis, and inflammationa

• Zona reticularis: innermost zone of adrenal cortex → secretes gonadocorticoids and glucocorticoids & an example is androgen and estrogen

What is the adrenal medulla, what does it consist of, and what hormone does it secrete and derived from? An example?

The deep region/core of adrenal gland. Consist of modified postsynaptic sympathetic neurons that secrete adrenal catecholamines derived from amino acids. An example is epinephrine and norepinephrine → which are secreted in response to sympathetic stimulation (flight/fight)

How are adrenal catecholamines and neuronal catecholamines similar and different

Adrenal catecholamines have the same effect on their target cells as neuronal catecholamines like dilation of the bronchioles, increase in rate/force of contraction of heart, constriction of blood vessels serving skin & abdominal viscera, dilation of pupils.
However, adrenal catecholamines prolong sympathetic response (neuronal catecholamines are terminated only after a few seconds) and can act on target cells not innervated by sympathetic neurons

What is the pancreas and where is it located. What functions does the pancreas have?

An elongated and spongy gland located below and behind the stomach. It has both endocrine and exocrine functions

What is the endocrine functions of the pancreas

Carried out by small round islands called pancreatic islets that are embedded in pancreatic acini. Cells in pancreatic islets secrete insulin and glucagon which regulate blood pressure

What are the antagonists of blood glucose levels, how are they produced and function?

Insulin: produced by beta (β) cells → triggers uptake of glucose by cells which decreases concentration of glucose in blood
Glucagon: produced by alpha (α) cells → triggers release of stored glucose from liver and production of new glucose increasing concentration of glucose in blood

Describe the testes

Male reproductive organs located in scrotum that produce sperm cells (male gametes). Cells in testes are called interstitial cells that produce testosterone → which promote production of sperm cells & development of male secondary sex characterisitics (deeper voice, greater bone, muscle mass, facial hair)

Describe the ovaries

Female reproductive organs located in pelvic cavity that produce oocytes (female gametes). Produce estrogen and progesterone → estrogen: play a role in development of oocytes, female secondary sex hormones (breast, subcutaneous fat stores) and progesterone: prepares body for pregnancy

How do you know that you are looking at histology of thyroid glands

Based on the colloid being surrounded by follicle cells and parafollicular cells

How do you know you are looking at histology of adrenal glands and how do you orientate yourself

Based on the layers and the thick zona fasciculata layer. You orientate yourself by finding the adrenal capsule (looks like strings) which indicated the superficial layer

How do you know you are looking at histology of the pancreas

By the pancreatic islet as it is lighter color and has multiple cells inside

The is the stimulus for secretetion of the negative feedback loop and examples

A disturbance in the homeostasis of a particular physiological variable like blood pressure, concentration of glucose in blood, and body temperature

What is the hormone’s response in the negative feedback loop

To act on distant target cells to cause changes that restore the variable to its normal range

What happens when homeostasis is restored in the negative feedback loop

The activity of the glands and concentration of the hormone declines → this is called negative feedback loop

What does negative feedback loop ensure

When a hormone level is high, its secretion remain low. If a secretion drops, then a stimulating hormone’s secretion rises, which stimulate an endocrine organ to secrete more hormone

What is an example of the negative feedback loop when concentration of glucose in the blood falls?

Start: concentration of glucose in blood falls → pancreas releases glucagon → level of the hormone glucagon in blood rises → hormone glucagon causes glycogenolysis by liver → concentration of glucose in blood rises → level of glucagon in blood decreases → End

What is exocrine function of the pancreas

Carried out by a group of cells called pancreatic acini or acinar cells, which occupies about 99% of the gland and release pancreatic juices into pancreatic ducts. These pancreatic juices contribute to neutralizing hydrochloric acid, digesting protein, fat, and starches.