Hormonal Regulation

Define Homeostasis

• Maintanance of an internal environment despite changes in the external environment.

Types of cell-cell communication

• Endocrine: hormone enters blood and acts on distant target cells.

• Paracrine: signalling molecule acts locally on neighbouring cells.

• Autocrine: cell signals back to itself; this can help limit its own hormone release.

• Synaptic/neural: a neuron releases a neurotransmitter across a tiny synaptic gap to a nearby target cell.MB_metabolic_hormones-2.pptx

Distinguish between nervous and endocrine systems

What are the two types of hormones?

What are the two transport mechanisms for hormones?

• Water soluble hormones: circulate in free form in the blood

• Lipid soluble hormones: must attatch to a transport protein which is synthesised by the liver.

What do transport proteins do?

Improve transport by making hormones water soluble and prevent loss of of the hormone by filtration in the kidney.

What are steroid receptors?

• Hormone bound steroid receptors are transcripts factors that regulate gene expression in a DNA sequence-specific manner.

Other types of receptors?

How can substances acting on steroid receptors cause toxicity?

They can mimic, block, or excessively stimulate hormone signalling, altering gene expression and disrupting development, reproduction, or normal hormonal feedback. Examples include DDT, DES, and anabolic-steroid misuse.

What are 4 hormonal interactions?

Interaction	Meaning	Example from the lecture
Permissive	One hormone must be present for another to exert its full effect	Thyroid hormone permits epinephrine to increase energy consumption
Synergistic	Two hormones together cause a larger response than their separate effects added together	Estrogen and LH together support oocyte production
Antagonistic	Hormones have opposing effects	Insulin promotes glycogen synthesis; glucagon promotes glycogen breakdown
Integrative	Several hormones jointly produce coordinated, tissue-specific outcomes	Most real physiological hormone responses

Can you explain the feedback mechanisms of hormones and give examples?

Negative: When a hormone’s effect restores the controlled variable—or when the final hormone level becomes high—the system reduces further hormone release.

• Higher testosterone feeds back to inhibit LH release, preventing excessive testosterone production.

Positive (less common): amplifies rather than corrects a change.

• A key example occurs near ovulation: rising estrogen can stimulate an LH surge, which drives ovulation.

Distinguish between autocrine feedback and target cell feedback.

• Autocrine feedback: an endocrine cell’s hormone inhibits further release from that same type of cell.

• Target-cell feedback: hormone A stimulates a target organ to produce hormone B, and hormone B inhibits hormone A

Hypothalamus and Pituitary importance

The hypothalamus receives neural and hormonal information from many brain regions, so it links nervous-system inputs to endocrine outputs.

Together with the pituitary, it coordinates other endocrine glands and is often called a master regulatory system.

What are the key differences between the two parts of the pituitary?

How does vasopressin increase water reabsorption in the kidney?

Vasopressin binds V2 receptors on collecting-duct principal cells, activating Gs​ → adenylyl cyclase → cAMP → PKA.

PKA promotes insertion of AQP2 water channels into the apical membrane, allowing water to move from tubular fluid back into blood.

What stimulates vasopressin release?

Increased plasma osmolarity, decreased blood volume/pressure, and angiotensin II.

Vasopressin increases kidney water reabsorption, producing less, more concentrated urine.

What is the angiotensin-aldosterone system?

The diagram shows how the body restores low blood pressure:

1. The kidney releases renin.

2. Renin converts angiotensinogen → angiotensin I; ACE converts it → angiotensin II.

3. Angiotensin II causes:

• Vasoconstriction → narrower blood vessels.

• Aldosterone release → kidneys retain sodium.

• Vasopressin release → kidneys retain water.

→ Together, these raise blood volume and blood pressure. Remember: aldosterone saves salt; vasopressin saves water.

Diabetes insipidus and the two types?

It is a failure to concentrate urine due to impaired vasopressin signalling, causing very high urine output and intense thirst.

Type	Problem	Typical cause in the slides
Central DI	Too little vasopressin is released	Damage to hypothalamic magnocellular neurons, tumours, or genetic abnormalities
Nephrogenic/peripheral DI	Kidney does not respond to vasopressin	V2 receptor defects or insufficient aquaporin insertion

In generl how much of metabolic activity results in heat and energy?

60% is heat and 40% is energy.

Distinguish betwene endocrine and exocrine function

• An exocrine function: acinar cells make digestive enzymes released into the gut.

• An endocrine function: islets of Langerhans release hormones into blood.

What are the 4 kinds of pancreatic islet cells?

Islet cell	Hormone	Core effect
α-cell	Glucagon	Raises blood glucose by stimulating liver glucose production and release
β-cell	Insulin	Lowers blood glucose by increasing glucose uptake, use, and storage
δ-cell	Somatostatin/GH-IH	Inhibits insulin and glucagon release
F/PP cell	Pancreatic polypeptide	Helps regulate pancreatic digestive functions

What happens in the pancrease during fed state? (repetition)

When blood glucose rises after a meal, pancreatic β-cells release insulin. Insulin promotes:

• Glucose uptake by insulin-responsive tissues, especially skeletal muscle and adipose tissue.

• Glucose utilisation and ATP production.

• Glycogen formation in liver and skeletal muscle.

• Triglyceride synthesis in adipose tissue.

• Amino-acid uptake and protein synthesis

What happens in the pancrease during starvation state?

When blood glucose falls, pancreatic α-cells release glucagon. Its primary metabolic target is the liver, where it promotes:

• Glycogen breakdown, releasing glucose.

• Gluconeogenesis, synthesising glucose from non-carbohydrate precursors.

• Release of glucose into blood.

• Mobilisation of fat stores, providing fatty acids as fuel.

Diabetes mellitus

Diabetes mellitus occurs when insulin is absent, inadequate, or ineffective, so glucose accumulates in blood rather than being taken up and used adequately by tissues.

High glucose can exceed the kidney’s capacity to reclaim it, causing glucosuria. Glucose in urine pulls water with it, causing polyuria.

Tissues may then increase fat and protein breakdown because they are relatively unable to access or properly use glucose.

Types of Diabetes Mellitus

Type	Core defect	Typical management concept
Type 1 diabetes	β-cells produce too little insulin, commonly due to autoimmune destruction	Requires insulin replacement
Type 2 diabetes	Insulin resistance, often with progressive β-cell dysfunction	Lifestyle changes, medications, and sometimes insulin

What is the effect of diabetes mellitus?

• Causes peripheral tissue damage

  • Diabetic nephropathy

  • peripheral neuropathy

  • retinopathy and heart problems