Homeostasis of Plasma Calcium and Plasma Glucose Concentrations Flashcards
What glands/organs are involved in the homeostasis of plasma calcium concentration?
Thyroid gland, parathyroid glands, and kidneys
Why is plasma [Ca2+] regulated?
Because there need to be enough Ca2+ calcium in the blood for cells to use it when they need it
How does the body use Ca2+?
- In the action mechanism for water soluble hormones (when the G-protein activates or inhibits 2nd messengers [cyclimAMP or Ca2+]. 2nd messengers affect actions of other proteins [eg. enzymes or ion channels])
- Ca2+ interacts with vesicles to facilitate release of neurotransmitter
- Ca2+ interacts with myofilaments in sarcomeres to facilitate cross-bridge formation (Note: all muscles require Ca2+ for tension creation)
- More than 99% of Ca2+ in the body is stored in bones (as hydroxyapatite)
- Ca2+ is very important to make bones hard and strong
- Bones act as Ca2+ reservoir
How does Ca2+ enter and exit the blood plasma?
Enters through:
- Ca2+ in food enters the digestive tract. Ca2+ is absorbed into blood from digestive tract
- Ca2+ is reabsorbed into blood from bone broken down by osteoclasts
- Ca2+ reabsorbed back into blood by kidneys
Exits through:
- Ca2+ removed from blood and deposited into bone by osteoblasts during remodelling and growth
- Ca2+ filtered out of blood by kidneys
Which glands/organs and hormones are involved in plasma [Ca2+] homeostasis?
Parathyroid glands, Kidneys, Thyroid gland, Bones and Digestive system.
Parathyroid glands:
- Parathyroid glands (x4) are the endocrine glands on the posterior of the thyroid gland
- Secrete Parathyroid Hormone (PTH)
- PTH is the most important hormone for [Ca2+] homeostasis
Kidneys:
- Kidneys (x2) anterior to lower ribs (posterior view)
- Stimulated by PTH to secrete Calcitriol
- Filter blood to make urine
- thus are also the sites for filtration of Ca2+ out of and reabsorption of Ca2+ back into the blood
Thyroid gland:
- Wraps around trachea/windpipe in the throat
- Secretes Calcitonin
- Calcitonin plays a very minor role in [Ca2+] homeostasis
Bones:
- Osteoblasts remove Ca2+ from plasma, to store in bone
- Osteoclasts release Ca2+ into plasma when breaking down bone
- Parathyroid, Calcitriol and Calcitonin affect those processes
Digestive system:
- Absorbs nutrients from food it has digested
- Absorbed Ca2+ enters the bloodstream
- Ca2+ absorption is increased under the influence of Calcitriol
How does the body correct hypocalcemia (low plasma [Ca2+])?
- Parathyroid glands (sensor & control centre)
- detect low Ca2+, compares to set point, then releases more Parathyroid Hormone (PTH) - Bone, Kidneys and Digestive tract (effectors)
- Bone: more Ca2+ resorbtion by osteoclasts = more Ca2+ into plasma
- Kidneys: more Ca2+ reabsorbition from pre-urine filtrate = more Ca2+ into plasma.
& More Vitamin D converted into Calcitriol (which acts on all three of these effectors)
- Digestive tract: more Ca2+ absorption from food = more Ca2+ into plasma - Plasma [Ca2+] increases
This is a negative feedback loop. When plasma Ca2+ increases it negatively feeds back to reduce PTH release again
What is the way that the body corrects hypercalcemia (high plasma [Ca2+]) with the bigger impact?
- Parathyroid glands (sensor and control centre)
- Detect high Ca2+, compared to set point, then release less Parathyroid Hormone (PTH) - Bone, Kidneys, Digestive Tract (effectors)
- Bone: less Ca2+ resorption by osteoclasts = less Ca2+ into plasma
- Kidneys: less Ca2+ reabsorption from pre-urine filtrate = less Ca2+ into plasma
& Less Vitamin D converted to Calcitriol. So it acts less on all three effectors (has less of an effect)
- Digestive tract: less Ca2+ uptake/absorbtion from food = less Ca2+ into plasma - Plasma [Ca2+] decreases
What is the way that the body corrects hypercalcemia (high plasma [Ca2+]) with the smaller impact?
- Thyroid gland (sensor and control centre)
- Detect high Ca2+, compares to set-point, then release Calcitonin - Bone and Kidneys (effectors)
- Bone: less Ca2+ resorption by osteoclasts = less Ca2+ into plasma
- Kidneys: less Ca2+ resorption from pre-urine filtrate = less Ca2+ into plasma - Plasma [Ca2+] decreases
What glands/organs are involved in homeostasis of plasma glucose concentration?
Pancreas (pancreatic islets)
Why is plasma glucose concentration regulated?
Because there needs to be enough glucose in the blood for cells to use it when they need it
How does the body use glucose?
- All body cells use glucose as the main substrate for making ATP
- Glucose is also used to make other substances essential for body functioning (eg. glycoproteins)
- Glucose is stored in the form of glycogen (long chains of glucose molecules) or fat
How does glucose enter or exit the blood plasma?
Enter:
- Carbohydrates in food enter digestive tract. Glucose absorbed into blood from the digestive tract
- Glucose released into blood by liver (new or from glycogen breakdown)
Excess intake of glucose over a long periods of time (years) can lead to disease: insulin resistance and type 2 diabetes
Exit:
- Glucose removed from blood by all body cells
- Excess glucose removed from blood and stored in liver and skeletal muscle as glycogen
- Excess glucose removed from blood and stored in adipose as fat
Cells use more glucose during periods of growth, stress and exercise and with higher metabolism
Which glands/organs and hormones are involved with [glucose] homeostasis?
Pancreas:
- The pancreas sits just behind the stomach, on the left side of the abdomen
- The pancreas is the endocrine organ that secretes hormones from plasma [glucose] homeostasis
- Pancreatic islet cells secrete hormones: glucose and insulin
- Alpha islet cells secrete glucagon
- Beta islet cells secrete insulin
- During a fasting state (no food intake for 4+ hours… so plasma signals to the liver to reduce glucose into plasma)
- by creating new glucose
- by breaking down glycogen into glucose
- During a fed state (food recently eaten, so plasma glucose is high) insulin signals to:
- all body cells to use glucose to make ATP (energy)
- Liver and skeletal muscle cells store excess glucose as glycogen
- Adipose cells (fat) store excess glucose as fat
Memory hook: A comes before B in the alphabet. G comes before I in the alphabet. So alpha = glucagon. Beta = insulin
Describe the daily fluctuations in plasma glucose in terms of the fasting and fed states.
Fasting state: about four hours without food
Fed state: during or immediately after a meal
- Eating complex carbs causes less of a plasma glucose spike and subsequent drop
- Eating simple carbs causes more of a spike and sudden drop
Excersise can help bring plasma glucose concentration down after a meal
How does the body correct hypoglycemia (low plasma [glucose])?
- Alpha cells in Pancreas (sensor and control centre).
- Alpha islet cells in the pancreas detect low glucose, compare to set-point and release glucagon - Liver (effector)
- Gluconeogenesis: building new glucose molecules to release into blood
- Glycogenolysis: breakdown of glycogen to release more glucose into blood
- Ketone Synthesis: building ketones to release into blood
(Note: when glucose is unavailable, fat is broken down to create ketones, another energy source) - Plasma glucose concentration increases
This is a negative feedback loop. When plasma glucose increases it negatively feeds back to reduce glucagon release.
