Hormones of the Heart, Kidney and Gut, Receptors and Integration: Quick Revision

A brief note on Hormones of the Heart, Kidney and Gut, Receptors and Integration. Read it before a test. Try each question at the end before you open its answer.

Hormones outside the main glands

• Heart: the wall of the atrium makes ANF, which dilates the blood vessels and lowers the blood pressure.
• Kidney: erythropoietin stimulates erythropoiesis, the making of red blood cells.
• Gut: gastrin (gastric glands: HCl and pepsinogen), secretin (exocrine pancreas: water and bicarbonate), CCK (pancreas: enzymes; gall bladder: bile) and GIP (inhibits the stomach).
• Growth factors: help the growth and repair of tissues.

How a hormone acts

• A hormone acts only on cells with its specific receptor. A hormone-receptor complex forms.
• Groups: peptide, polypeptide or protein; steroid; iodothyronine; amino acid derivative.
• Membrane receptors (peptides, adrenaline): second messengers such as cyclic AMP, IP3 and Ca$^{2+}$.
• Intracellular receptors (steroids, thyroid hormones): the complex acts on the genome and regulates gene expression.

Integration

• The neural and endocrine systems together coordinate the body. The hypothalamus joins them.
• Negative feedback keeps a level near a set point. Positive feedback drives a process to its end, for example oxytocin in childbirth.
• Opposite pairs: insulin and glucagon, PTH and thyrocalcitonin.

A worked example

A receptor has a Kd of 4 nmol/L. The hormone is at 4 nmol/L. What share of the receptors is occupied?

1. The share is the hormone divided by (Kd plus hormone): $\dfrac{4}{4 + 4}$.
2. This is one half, or 50 per cent. At a concentration equal to the Kd, half of the receptors are occupied.

Practice with new numbers

A program to try

The program prints the share of receptors occupied for three concentrations.

Mistakes to avoid

• Saying that a peptide hormone enters the cell. It works through a receptor in the membrane and a second messenger.
• Saying that a steroid hormone has a receptor on the surface. Its receptor is inside the cell.
• Calling labour a negative feedback. It is a positive feedback.
• Saying that GIP stimulates the stomach. It inhibits the stomach.

Check yourself

1. Which hormone of the heart lowers the blood pressure?

2. Which kind of hormone has an intracellular receptor?

3. Which molecule is a second messenger of many hormones?

4. Which part of the brain joins the nervous system to the endocrine system?

Sources

• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 17.
• Alberts B. et al. (2022). Molecular Biology of the Cell, 7th edition, W. W. Norton.
• NCERT (2023). Biology, Textbook for Class XI, chapter 19.