14 – Ca, P, Vit D and Vit K Flashcards
(37 cards)
1
Q
What are the minerals and vitamins involved with Ca & P metabolism?
A
- Calcium
- Phosphate
- Vitamin D
- Vitamin K
2
Q
What are the functions of calcium?
A
- Bone strength and maintenance
- Can contribute to membrane potential
- Blood clotting (cofactor at multiple points)
- Serves as 2nd messenger to rely info form outside to inside the cell
- *major component of milk
3
Q
Absorption of calcium: 2 distinct mechanisms
A
- Active, transcellular absorption
a. Upregulated to increase Ca absorption when body Ca stores are low - Passive, paracellular absorption
a. Occurs all the time
b. Passive diffusion, so rate is dependent on dietary Ca concentration
4
Q
Where does passive paracellular absorption of Ca occur?
A
- Jejunum and ileum
- *When dietary calcium levels are moderate or high
5
Q
Passive paracellular absorption of Ca
A
- Diffuses through tight junctions into basolateral spaces around enterocytes and into blood
- Up to 50% absorption in monogastrics
- Less important in ruminants because rumen dilutes Ca in digesta
6
Q
Where does active transcellular absorption of Ca occur?
A
- Duodenum
- Up regulated when body Ca stores are low
7
Q
What are the 3 steps of active transcellular absorption of Ca?
A
- Facilitated diffusion of calcium into enterocyte
- Transport across the enterocyte
a. *regulated at this step
b. Controlled by amount of carrier protein calbindin present in cell
c. *Vit D activation of Vitamin D receptor (VDR) increases synthesis of calbindin - Active transport into ECF (ATP>ADP)
8
Q
What inhibits Ca absorption?
A
- Compounds that form insoluble Ca salts
o Oxalates, phytates, phosphates all form insoluble salts
o Undigested fats for Ca soaps - *large part of ingested Ca is NOT absorbed and is excreted in feces (low digestibility)
9
Q
What is the major Ca binding factor in the blood?
A
- Gamma-carboxyglutamate (Gla) residues in serum proteins (albumin)
- *vit K is a cofactor in the enzymatic production of Gla
10
Q
What can be seen with Vit K deficiency?
A
- Reduce bone density and cause osteoporosis
o Vit K need for gamma-carboxylation and activation of osteocalcin - Clotting deficiency
11
Q
Poisoning with Vit K antagonists (ex. warfarin and dicoumarol)
A
- Interfere with regeneration of Vit K by inhibiting its reductase
o Leads to deficiency of ACTIVE Vit K - *a single feeding of poisoned bait can kill the rodent, and also cause bleeding disease in wildlife, dogs, or cats that INGEST them
12
Q
Vitamin K deficiency: in different species
A
- Human newborns: have NO stores of Vit K
o If they don’t get a supplement=hemorrhagic disease of newborns can result
o Usually given a 1mg injection of Vit K at birth - Deficiencies are rare in ruminants and non-human monogastrics
- Deficiency in chickens and pigs leads to spontaneous hemorrhages
13
Q
What are some sources of Vit K?
A
- Plants and bacteria
o Intestinal synthesis is important (ruminants do NOT require additional Vit K) - High levels of feed antibiotics may reduce Vit K synthesis
- Synthetic source: menadione
o Susceptible to oxidation if exposed to sunlight, moisture, choline or trace elements
14
Q
How is calcium excreted? (3)
A
- Kidney
a. Excreted this way when calcium concentration in serum is high
b. Tightly regulated - Secretion into intestinal lumen when calbindin is downregulated (epithelial cells are sloughed and unabsorbed Ca goes with them)
a. FECAL excretion - Sweat (small amount)
15
Q
Calcium levels in body/storage
A
- 99% in bones and teeth (hydroxyapatite)
- Bone resorption changes with Ca
o Osteoclasts remove Ca-P from bone
o Osteoblasts deposit Ca-P in bone
16
Q
What are the 3 ways calcium levels are regulated?
A
- PTH: secreted when Ca low
a. Rapid and slower effects - Vit D
- Other hormones: calcitonin, estrogen
17
Q
PTH: rapid effects
A
- Increases Ca reabsorption across the renal glomerulus
- Decrease urinary Ca loss
18
Q
PTH: slower effects
A
- Stimulates production of Vit D in kidney
- Vitamin D3 increases rate of intestinal Ca absorption
- Increase release of bone Ca stores (recruits osteoclasts)
19
Q
Where are Vit D precursors found?
A
- Plant and animal tissues
o Plant: ergosterol
o Animals: 7-dehydrocholesterol - *converted to Vit D by sunlight UVB on the skin
o Activation may be impaired by fur coat or when animals are indoors
20
Q
What are the steps of how Vit D works with PTH to regulate Ca and P metabolism?
A
- Increases Ca absorption
- Induces gut epithelial calbindin expression
- Increases P absorption
- Stimulates synthesis of collagen and other bone matrix proteins by osteoblasts
- Stimulates bone resorption by osteoclasts and stimulates osteoclast recruitment
- **Net effect is higher blood Ca concentrations
21
Q
Calcitonin
A
- Important in fish
- Relatively unimportant in terrestrial animals
- Has opposite effect of PTH
22
Q
Estrogen
A
- Regulates osteoclast and osteoblast populations
- When levels are low=more bone reabsorbed (can lead to osteoporosis)
o Supplemental estrogen prevents osteoporosis in postmenopausal women
23
Q
What are the functions of phosphorus?
A
- Most abundant intracellular anion (phosphate)
- Structural: essential part of bone mineral (75-85%)
- Remaining 15-25% is in soft tissues
24
Q
Phosphorus functions in soft tissues
A
- Component of cell membranes (phospholipids)
- Metabolic: ATP, RNA, DNA, NADP, etc
25
Phosphate intestinal absorption (similar to Ca)
- Passive paracellular diffusion
- Active transcellular transport
o Actively stimulated by Vit D
- **excretion and absorption regulated by PTH and Vit D
26
PTH, Vit D and P regulation: when [P] in blood is low
- Stimulates Vit D3 production
- *decreases PTH secretion
- Increases intestinal absorption of P
- Increases serum [P]
27
PTH, Vit D and P regulation: when [P] in blood is high
- Increases PTH secretion and decreases Vit D3 production
o Have a ‘fighting effect of Vit D”
- ***PTH decreases renal absorption of P (PEE out your P)
- Decreases serum [P]
28
When does the regulation of Ca and P work well in terms of Ca:P ratio in diet?
- 1.2:1 to 2:1
o *maximize Ca absorption in monogastrics
29
Excessive dietary P can interfere with Ca absorption in small intestine
- Most phosphate salts are highly insoluble in water (ex. calcium phosphate)
- Animals and plant ingredients both have phosphates
o Animal P is lower and more digestible=more readily absorbed
- High dietary phytate is problematic
- *high dietary P levels lead to large fecal losses and bone resorption
30
Phytate
- High dietary phytate is problematic
- *phytate is mostly insoluble, phosphate rich plant compound
o Binds dietary cations=prevents absorption
- Found in bran or husk of many grains, legumes and seeds
- *can treat plant-based feed ingredients with PHYTASE to reduce phytate levels and free phosphate
31
32
What are your sources of Ca?
- Insufficient in plant sources
- *to get a balanced Ca-P ratio, normally add
o Meat meal for protein/P
o Dicalcium phosphate for P
o Limestone or calcium carbonate (oyster shells) to balance Ca:P ratio (No P in there)
- Can use bone meal for P and has some Ca=but more useful as a P source
- *Ca is cheap and P is expensive
33
Ca, Vit D, Phosphorus deficiency
- Similar symptoms for all 3 nutrients
- Difficult to distinguish one from another w/o doing blood chemistry
- Osteoporosis: brittle bones
- *rickets in young and osteomalacia and poor pigmentation in older animals
o Abnormalities of erythrocytes, leukocytes and platelets
o Pica (behaviour_ where animals consume dirt or chew on pen materials
34
When does cage layer fatigue occur? Why does it occur? What does it cause?
- Occurs in laying hens at peak production
- Due to high requirement for Ca for egg shell formation
- *Causes bone deformities, fractures and paralysis
- Pullets should be fed high Ca to build up reserves and proper Ca, P and Vit D levels should be maintained in diet
o “bone bank”
35
Ca toxicity
- Does not occur normally
- *excess Ca is simply NOT absorbed
36
P toxicity
- Rare
- Usually due to kidney failure
37
Vit D toxicity
- Calcification of soft tissue
o Hypertension
o Renal failure
- Avoid megadose of vit D
- Toxicity often due to errors in calculation/unit interpretation during feed formulation
