The endocrine system (3) Flashcards
Week 7
Colour of parathyroid cells and location.
Tiny, yellow-brown glands embedded in posterior aspect of thyroid
What do parathyroid cells secrete?
Parathyroid hormone (PTH) of parathormone
Why is PTH important in Ca2+ homeostasis? (2)
- Secreted in response to low blood levels of Ca2+
- Inhibited by rising levels of Ca2+
What are the target organs for PTH?
Skeleton, kidneys and intestine
What happens when Ca2+ levels drop in the blood (Hypocalcemia) and there is an increase in PTH released from parathyroid gland (3 different ways)
1- Increase in osteoclast activity in bone causes Ca2+ and PO(4)3- release in blood = increase in Ca+ in blood.
2- Increase in Ca2+ reabsorption in kidney tubule = increase in Ca2+ in blood.
3- Increase in activation of vitamin D by kidney = increase in Ca2+ absorption from food in the small intestine = increase in Ca2+ in blood.
What happens when there is an increase in Ca2+ levels in the blood? (4 steps)
- Thyroid gland releases calcitonin.
- Calcitonin stimulates Ca2+ deposition in bones and reduces Ca2+ uptake in kidneys
- Blood Ca2+ level declines to set point
- Homeostasis is reached for blood Ca2+ levels, about 10mg/100 mL
What happens when there is a decrease in blood Ca2+ levels?
- The thyroid gland releases PTH.
- PTH stimulates Ca2+ release from bones.
3, PTH stimulates Ca2+ uptake in kidneys which produces active vitamin D which increases Ca2+ uptake in the intestines. - Blood Ca2+ level rises to set point.
- Homeostasis is reached for blood Ca2+ levels, about 10mg/ 100 mL
Describe Parafollicular cells and what they secrete?
-Small, round cells found in between colloid-filled follicles.
-They secrete calcitonin
Describe Follicular cells and what they secrete?
-Small round cells found in the membranes in colloid-filled follicles.
-They secrete thyroid hormone
