Feedback Loops of the Endocrine System + Stress

SBI4U Howes

Endocrine vs Exocrine Glands

Endocrine: secretes hormones directly into bloodstream

Exocrine: secretes hormones through a duct or similar structure

Name the hormones that regulate blood sugar (3)

• Insulin

• Glucagon

• Glucocorticoids (mainly cortisol)

Insulin is produced in the pancreas, specifically in ____ ___________ called the:

Cell clusters, islets of Langerhans

when is insulin secreted?

in response to raised blood glucose levels

i.e. after a meal

what does insulin do?

instructs cells to take in blood’s glucose: LOWERS blood glucose

besides lowering blood glucose, what else does insulin do?

promotes protein synthesis and storage of lipids while inhibiting their breakdown (to fatty acids)

“Body doesn't need alt. fuel, so it will store the fuel instead”

where is glucagon produced?

islets of Langerhans (pancreas) — alpha cells

when is glucagon secreted?

in response to reduced blood glucose levels

i.e. following an exercise or missing a meal

what does glucagon do?

raises blood glucose by stimulating breakdown of glycogen (a glucose-storing molecule)

besides breaking down glycogen, what else does glucagon promote the breakdown of?

fats → fatty acids

proteins → amino acids

the other kind of glucose regulators are:

glucocortinoids!

unlike insulin and glucagon, which are produced in the ___________, glucocorticoids are produced by the ________ _________.

pancreas, adrenal cortex

explain the three ways cortisol raises blood sugar

1. Stimulates glucose synthesis from lipid and protein sources

2. Reduces glucose uptake by the body's cells **except for CNS cells

3. Promotes breakdown of proteins, lipids (into amino acids/fatty acids)

3 kinds of diabetes mellitus

• Type 1

• Type 2

• Gestational

type 1 cause + treatment

• β-cells in pancreas unable produce to insulin

• monitoring blood glucose, take reg insulin injections (or perm. pump!)

type 2 cause + treatment

• low insulin sensitivity; can be caused by reduced insulin production or by weak response

• medications or lifestyle changes

Gestational cause + treatment

• rare, due to higher blood glucose during pregnancy

• typically goes away on its own

The endocrine system uses many feedback loops; explain one related to TSH

hypothalamus → TRH → pituitary → TSH → thyroid → thyroid hormones (inhibit secretion of TSH)

describe the negative feedback loop in calcium-related hormones.

• rising calcium in the blood → thyroid gland → calcitonin (Ca2+ declines)

• falling calcium in blood → parathyroid gland → PTH (Ca2+ rises)

basically, the rise of Ca2+ inhibits the parathyroid gland, and the fall of Ca2+ inhibits the thyroid gland

recall that homeostasis is regulated by _ systems:

2, NERVOUS & ENDOCRINE

Stress

the body’s response to stimuli/stressors, that cause a disruption to homeostasis (the body is trying to return to homeostasis)

stress can be both positive (_______) or negative (________)

eustress, distress

other categories of stress:

• physical vs emotional vs psychological

• short-term vs long-term

in extreme cases where stress has _________ long after the ________ was removed, this is called ______

lingered, stressor, PTSD

3 stages to stress

1. Alarm Reaction: body recognizes a stressor and prepares for defense ⏰

2. Resistance: body adapts and aims to restore balance ⚔️

3. Exhaustion: occurs if the body's resources are depleted 🥱

outline the body’s response to short-term stress

adrenal medulla procudes epinephrine + norepinephrine

⇨ result is ↑ breathing, heart rate, blood glucose, cell metabolism, dilation of pupils & blood vessels

outline the body’s response to short-term stress

adrenal cortex produces mineralocortinoids + glucocortinoids (ex: cortisol)

⇨ result is ↑ sodium and water is reabsorbed in the kidneys

⇨ result is ↑ blood glucose, ↓ insulin production, ↓ inflammatory response of the immune system