homeostasis: the liver and pancreas
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Homeostasis: the liver and pancreas. CHAPTER 4.2. Overview. Mammalian Liver Anatomy Functions Lipid Regulation Protein and Amino Acid Regulation Blood Sugar regulation Bile production Other functions Chemical classification of Hormones Water and lipid soluble hormones - PowerPoint PPT PresentationTRANSCRIPT
HOMEOSTASIS:THE LIVER AND PANCREAS
CHAPTER 4.2
Overview Mammalian Liver
Anatomy Functions
Lipid Regulation Protein and Amino Acid Regulation Blood Sugar regulation Bile production Other functions
Chemical classification of Hormones Water and lipid soluble hormones Hormonal Feedback loop Antagonistic Hormones
Mammalian Pancreas Blood sugar regulation
Liver: Bodily Metabolic Centre
Largest gland in the body with many metabolic and regulatory roles
Lies on the upper right section of the abdominal cavity, under the diaphragm
Receives plentiful blood supply where substances are extracted for processing. 2 main vessel:- Hepatic artery – brings oxygenated blood from dorsal artery Hepatic portal vein – bring nutrient rich blood from small
intestines Hepatic vein - Blood from liver is brought back to heart
via this vein and posterior vena cava.
Liver cell/hepatocytes are undifferentiated and structurally identical.
Contains approximately 0.1 millions lobules that serve as structural and functional units Each lobe contains rows of liver cells
1. Liver artery arm2. Bile duct 3. Bile duct arm4. Portal vein a. Lobe (simplified) b. Hepatocyte
Functions of the Liver Over 500 functions. Most importantly
Regulation of lipids Lipids used for energy for cellular functions (more energy
than glucose) Liver responsible for proper lipid concentrations in the blood. Lipids removed from blood by liver cells or transported to fat
storage areas in the form of adipose tissue or lipoproteins for brain and nerve tissue synthesis
Cholesterols removed and some converted to bile salts Fatty acids conversion to acetyl-coA via fatty acid
spiral/lipolysis Lipid synthesis – cholesterol synthesis (Mevalonate
pathway) and lipogenesis Abnormally high lipids – arthrosclerosis, coronary thrombosis
Functions of Liver
Regulation of amino acids and proteins Non-essential aa can be synthesised by
transamination
Excess aa and proteins cannot be stored in the body. Any excess in returned to the liver for catabolism through deamination into non-nitrogenous and nitrogenous parts (amino group - NH2)
The non-nitrogenous, keto acid is converted into glucose in the liver to be stored as glycogen or broken down to release heat.
The nitrogenous ammonia, is potently toxic. Hence, it is converted into urea using the urea or ornithine cycle
This is transported by the blood the kidneys for excretion
+ ATP
Functions of Liver
Bile production Bile comprises of bile salts and bile
pigments that is stored in the gall bladder till needed in fat digestion
Bile salts are synthesized from cholesterol Bile pigments (yellowish-green) are from the
incorporation of the by-products of red blood cell disassembly
Gallstones are an accumulation of cholesterol crystals that can cause blockage of the bile/biliary duct and increase pressure of the gall bladder.
Accumulation stems from bile constituents’ imbalance.
Functions of Liver
Regulation of blood sugar level Excess glucose is either converted by pancreatic
insulin for storage as glycogen; or broken down into H2O + CO2 + heat
When the body has excess glucose, glycogenesis is the synthesis of glycogen from glucose that is stimulated in the presence of the pancreatic hormone insulin.
Prevention of glucose from falling below the crucial level is performed by a process called glycogenolysis.
Glycogenolysis is the catabolism of glycogen that requires the activation of hepatic enzyme glycogen phosphorylase by pancreatic hormone glucagon.
Hexokinase is stimulated by insulin
Glycogen phosphorylase is stimulated by glucagon
Functions of Liver
Regulation of blood sugar level In skeletal muscles, glycogen cannot be
converted into glucose directly through glucose-6-phosphate route as in the liver due to the lack of the enzyme glucose-6-phosphotase.
Instead it is channeled through glycolysis and converted into pyruvate. Consecutively, processed through aerobiosis or anaerobiosis.
In anaerobiosis, lactate that will be carried to the liver for conversion – firstly, to glucose and then glycogen using the Cori cycle.
Cori Cycle
Functions of Liver
Thermoregulation Liver is large Plenty of blood and high metabolic rate Hence, easy to release excess heat to maintain body
temperature.
Detoxification of blood – Kupffer cells Elimination of steroids Storage of blood Formation of red blood cells in foetus Production of plasma protein (fibrinogen,
albumin and globulin) Storage of vitamins and minerals
Chemical Classes of Hormones
Three major classes of molecules function as hormones in vertebrates: Polypeptides (proteins and peptides) Amines derived from amino acids Steroid hormones
Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not
The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells
Fig. 45-3
Water-soluble Lipid-soluble
Steroid:Cortisol
Polypeptide:Insulin
Amine:Epinephrine
Amine:Thyroxine
0.8 nm
Cellular Response Pathways
Water and lipid soluble hormones differ in their paths through a body
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells
Fig. 45-5-2
Signalreceptor
TARGETCELL
Signal receptor
Transportprotein
Water-solublehormone
Fat-solublehormone
Generegulation
Cytoplasmicresponse
Generegulation
Cytoplasmicresponse
OR
(a) NUCLEUS (b)
Negative feedback and antagonistic hormone pairs
Hormones are assembled into regulatory pathways
Hormones are released from an endocrine cell, travel through the bloodstream, and interact with the receptor or a target cell to cause a physiological response
A negative feedback loop inhibits a response by reducing the initial stimulus
Negative feedback regulates many hormonal pathways involved in homeostasis
Fig. 45-11Pathway Example
Stimulus Low pH induodenum
S cells of duodenumsecrete secretin ( )
Endocrinecell
Bloodvessel
PancreasTargetcells
Response Bicarbonate release
Neg
ati
ve f
eed
back
–
Insulin and Glucagon: Control of Blood Glucose
Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis
Glucose that is absorbed from the gut into the hepatic portal vein, increases the blood glucose concentration. This is detected by the pancreas
The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin
Pancreas: Endo- and Exocrine Functions Lies deep within the abdominal cavity, on the
posterior of the abdominal wall Elongated and somewhat flattened organ with
endo- and exocrine functions. As an exocrine gland, it functions in the
digestive system due to the secretion of pancreatic juice via the ducts to the small intestines.
As an endocrine gland, it function in the secretion of hormones (insulin, glucagon and somatostatin)
This is thanks to the cells on the islet of Langerhans
Fig. 45-12-1
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells ofpancreasrelease insulininto the blood.
STIMULUS:Blood glucose level
rises.
Fig. 45-12-2
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells ofpancreasrelease insulininto the blood.
STIMULUS:Blood glucose level
rises.
Liver takesup glucoseand stores itas glycogen.
Blood glucoselevel declines.
Body cellstake up moreglucose.
Fig. 45-12-3
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:Blood glucose level
falls.
Alpha cells of pancreasrelease glucagon.
Fig. 45-12-4
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:Blood glucose level
falls.
Alpha cells of pancreasrelease glucagon.
Liver breaksdown glycogenand releasesglucose.
Blood glucoselevel rises.
Fig. 45-12-5
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:Blood glucose level
falls.
Alpha cells of pancreasrelease glucagon.
Liver breaksdown glycogenand releasesglucose.
Blood glucoselevel rises.
STIMULUS:Blood glucose level
rises.
Beta cells ofpancreasrelease insulininto the blood.
Liver takesup glucoseand stores itas glycogen.
Blood glucoselevel declines.
Body cellstake up moreglucose.
Insulin
Target Tissues for Insulin and Glucagon
Insulin reduces blood glucose levels by Promoting the cellular uptake of glucose Slowing glycogen breakdown in the liver Promoting fat storage (lipogenesis)
Glucagon increases blood glucose levels by Stimulating conversion of glycogen to glucose in the
liver Stimulating breakdown of fat and protein into
glucose
Diabetes Mellitus
Diabetes mellitus is perhaps the best-known endocrine disorder
It is the failure of glucose homeostasis
It is caused by a deficiency of insulin or a decreased response to insulin in target tissues
It is marked by elevated blood glucose levels
Type I diabetes mellitus (insulin-dependent) (30%) is an autoimmune disorder in which the immune system destroys pancreatic beta cells
Type II diabetes mellitus (non-insulin-dependent) (70%) involves insulin deficiency or reduced response of target cells due to change in insulin receptors
Diabetes Mellitus
You should now be able to:
1. Note the anatomy and function of the liver lobules and their components
2. Difference in canaliculi and sinusoid.3. Distinguish between the major functions
of the liver especially lipid, protein, amino acids and glucose regulation.
4. Describe the difference between water-soluble and lipid-soluble hormones
5. Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism
6. Distinguish between type 1 and type 2 diabetes