Chapter 5.2 - Regulation of Blood Sugar

Sugar in the blood is in the form of glucose. blood sugar = the amount of glucose in the blood

• All cells need a constant supply of glucose • Because it is the SOURCE OF ENERGY for all cell activities • eg movement, reproduction, synthesizing molecules active transport, + others ENERGY IS RELEASED FROM GLUCOSE MOLECULES BY CELLULAR RESPIRATION

GLUCOSE + OXYGEN —> CARBON DIOXIDE + WATER + ENERGY

body’s SOURCE of GLUCOSE is in the FOOD WE CONSUME • CARBOHYDRATES in our food are BROKEN DOWN into GLUCOSE DURING DIGESTION, • then ABSORBED into the BLOOD through the WALLS of the SMALL INTESTINE. • after meal, BLOOD GLUCOSE CONT. can RISE SHARPLY • HOMEOSTATIC MECHANISMS then BEGIN to OPERATE to REDUCE the BLOOD GLUCOSE CONT. AND MAINTAIN it at a NORMAL LEVEL. • ANY EXCESS GLUCOSE in the blood must be REMOVED and STORED READY for use in CELLULAR ACTIVITIES between meals.

A POLYSACCHARIDE MADE UP OF 1000S OF GLUCOSE MOLECULES BONDED TOGETHER IN BRANCHING CHAINS: FUNCTIONS AS A STORE OF GLUCOSE MOLECULES IN MUSCLE AND LIVER CELLS GLUCOSE IN THE BODY IS STORED AS GLYCOGEN. GLYCOGEN IS A MOLECULE made up of LONG CHAINS of GLUCOSE MOLECULES. • Body is able to store about 500g of glycogen: • about 100g is stored in the liver • remainder in skeletal muscle cells • STORED IN THE LIVER

EXCESS GLUCOSE IN THE BODY IS CONVERTED TO GLYCOGEN FOR STORAGE. - BLOOD GLUCOSE LEVEL HIGH (eg. after a meal) Alternatively, GLYCOGEN CAN BE CONVERTED BACK TO GLUCOSE, when there is not enough glucose in the blood. - BLOOD GLUCOSE LEVEL LOW (eg. during exercise)

LOCATION - upper part of the abdominal cavity, below the diaphragm. WHAT - largest gland, which has an important role in the CONTROL OF BLOOD SUGAR CONT. ROLE - LIVER is able to CONVERT GLUCOSE –> GLYCOGEN FOR STORAGE, OR GLYCOGEN –> GLUCOSE FOR RELEASE into BLOOD. HOW? - • most of the liver’s SUPPLY VIA HEPATIC PORTAL VEIN, • BRINGS BLOOD DIRECTLY FROM THE STOMACH, SPLEEN, PANCREAS, SMALL AND LARGE INTESTINES. • SO THAT THE LIVER HAS THE 1ST CHANCE TO ABSORB THE NUTRIENTS FROM DIGESTED FOOD. • after a typical meal, containing a high portion of carbohydrates is consumed, THE BREAKDOWN PRODUCTS, MAINLY GLUCOSE, ARE ABSORBED INTO THE BLOOD CAPILLARIES OF VILI OF SM. INTST. GLYCOGEN • IS stored in the liver, for SHORT TERM ENERGY SUPPLY • can PROVIDE GLUCOSE FOR BODY CELL for 6 HOURS ONLY, if no other supply is available • if more energy required, the body uses the energy reserves in stored fat.

GLUCOSE MAY: • REMOVED FROM BLOOD by liver to PROVIDE ENERGY FOR LIVER FUNCTIONING • REMOVED by the LIVER and or MUSCLES and CONVERTED INTO GLYCOGEN FOR STORAGE. • CONTINUE, TO CIRCULATE in the BLOOD, - AVAILABLE FOR BODY CELLS TO ABSORB AND USE AS A SOURCE OF ENERGY. • CONVERTED into FAT for LONG TERM STORAGE, if it is IN EXCESS of that required to MAINTAIN BOTH NORMAL BLOOD SUGAR and TISSUE GLYCOGEN LEVELS.

GLUCOSE MAY: • REMOVED FROM BLOOD by liver to PROVIDE ENERGY FOR LIVER FUNCTIONING • REMOVED by the LIVER and or MUSCLES and CONVERTED INTO GLYCOGEN FOR STORAGE. • CONTINUE, TO CIRCULATE in the BLOOD, - AVAILABLE FOR BODY CELLS TO ABSORB AND USE AS A SOURCE OF ENERGY. • CONVERTED into FAT for LONG TERM STORAGE, if it is IN EXCESS of that required to MAINTAIN BOTH NORMAL BLOOD SUGAR and TISSUE GLYCOGEN LEVELS.

GLUCOSE MOLECULES ARE CHEMICALLY JOINED IN LONG CHAINS TO FORM GLYCOGEN MOLECULES. Formation of glycogen from other carbohydrates • IT IS STIMULATED BY THE PANCREATIC HORMONE - INSULIN • GLYCOGEN ITSELF CANNOT BE USED BY CELLS: IT MUST BE CONVERTED INTO GLUCOSE TO MAINTAIN BLOOD SUGAR LEVELS AND SUPPLY ENERGY FOR LIVER ACTIVITY • GLYCOGEN IN MUSCLE CELLS PROVIDES THE GLUCOSE REQUIRED FOR MUSCLE ACTIVITY

GLYCOGEN STORED IN THE LIVER AND MUSCLE CELLS CAN BE BROKEN DOWN INTO GLUCOSE. * GLYCOGENOLYSIS

THE PROCESS OF CONVERTING GLYCOGEN BACK INTO GLUCOSE • most frequently occurs between meals and is stimulated by the PANCREATIC HORMONE GLUCAGON.

IT IS THE CONVERSION OF FATS OR PROTEINS INTO GLUCOSE. • THE PROCESS OF PRODUCING GLUCOSE MOLECULES FROM LIPIDS AND AMINO ACIDS

LOCATION - LYING PARTLY in the CURVE of the DUODENUM. WHAT? pale grey gland, 12-15 cm long. JOB? Has ISLETS OF LANGERHANS - 2 TYPES: ALPHA secreting GLUCAGON BETA secreting INSULIN

Clusters of endocrine cells in the pancreas: secrete the hormones insulin and glucagon via the Beta and Alpha cells respectively.

A type of cell in the islets of Langerhans in the pancreas that secretes the hormone insulin.

A type of cell in the islets of Langerhans in of the pancreas that secretes the hormone insulin.

• accelerating the TRANSPORT OF GLUCOSE FROM THE BLOOD INTO BODY CELLS, ESPECIALLY IN SKELETAL MUSCLES 2. ACCELERATING CONVERSION OF GLUCOSE INTO GLYCOGEN IN THE LIVER AND SKELETAL MUSCLE. #GLYCOGENESIS • STIMULATING CONVERSION OF GLUCOSE INTO PROTEIN (PROTEIN SYNTHESIS) • STIMULATING THE CONVERSION OF GLUCOSE INTO FATS (LIPIDS), IN ADIPOSE TISSUE, OR FAT STORAGE (LIPOGENISIS)

The production of lipids (fats)

Stimulus - blood glucose levels rise above normal Receptor - Chemoreceptors in the beta cells Modulator - islets of Langerhans stimulate secrete INSULIN MESSAGE - insulin to be secreted EFFECTOR - SKELETAL MUSCLES, AND LIVER • accelerating the TRANSPORT OF GLUCOSE FROM THE BLOOD INTO BODY CELLS, ESPECIALLY IN SKELETAL MUSCLES 2. ACCELERATING CONVERSION OF GLUCOSE INTO GLYCOGEN IN THE LIVER AND SKELETAL MUSCLE. #GLYCOGENESIS • STIMULATING CONVERSION OF GLUCOSE INTO PROTEIN (PROTEIN SYNTHESIS) • STIMULATING THE CONVERSION OF GLUCOSE INTO FATS (LIPIDS), IN ADIPOSE TISSUE, OR FAT STORAGE (LIPOGENISIS) NEGATIVE FEEDBACK - Decrease in blood glucose level

The breakdown of lipids (fats) in the body.

• Stimulating GLYCOGENOLYSIS in the LIVER • Stimulating GLYCONEOGENESIS, in the LIVER - involves the breakdown of lipids in the process (LIPOLYSIS) • MILD STIMULATING EFFECT on PROTEIN BREAKDOWN. • THE GLUCOSE FORMED IS RELEASED INTO THE BLOOD, AND GLUCOSE LEVEL RISES

Stimulus - blood glucose levels decrease above normal Receptor - Chemoreceptors in the alpha cells Modulator - islets of Langerhans stimulate secrete GLUCAGON MESSAGE - GLUCAGON to be secreted EFFECTOR - SKELETAL MUSCLES, AND LIVER RESPONSE - 1. Stimulating GLYCOGENOLYSIS in the LIVER • Stimulating GLYCONEOGENESIS, in the LIVER - involves the breakdown of lipids in the process (LIPOLYSIS) • MILD STIMULATING EFFECT on PROTEIN BREAKDOWN. • THE GLUCOSE FORMED IS RELEASED INTO THE BLOOD, PRODUCTION REDUCED NEGATIVE FEEDBACK – GLUCOSE LEVEL RISES

The REGULATION of the SECRETION of GLUCAGON, like that of INSULIN SECRETION, is DIRECTLY DETERMINED BY THE LEVEL OF GLUCOSE IN THE BLOOD AND CONTROLLED BY A NEGATIVE FEEDBACK SYSTEM.