Comprehensive Guide to Glucose Homeostasis and OGTT for Biology Students

Main purpose of Lab 3: Glucose Homeostasis

To perform a glucose tolerance test, explore glucose homeostasis, and understand how research questions influence statistical test choices and data interpretation.

Specific goals of Lab 3

1. Identify stimulus, sensor, afferent signal, integrator, efferent signal, effector, and response. 2. Predict how control mechanisms alter variables (setpoints, feedback, feedforward, tonic, antagonistic control). 3. Describe blood glucose regulation and predict effects of perturbations. 4. Create and interpret an OGTT curve. 5. Explain GLUT vs SGLT in function and location.

antagonists

Two controllers act in opposite directions (e.g., sympathetic vs parasympathetic).

antagonistic control

Two controllers act in opposite directions (e.g., sympathetic vs parasympathetic).

afferent (input) signal

Carries information from sensor to integrator.

efferent (output) signal

Carries commands from integrator to effector.

stimulus

A detectable change in the internal or external environment.

sensor

Detects changes in the regulated variable.

integrator

Processes incoming signals and determines the response.

effector (target)

Cell/tissue that carries out the response.

setpoint

The ideal value a system tries to maintain.

regulated variable

The variable being controlled (e.g., blood glucose).

physiological response

The effect that restores balance.

hyperglycemia

High blood glucose levels.

hypoglycemia

Low blood glucose levels.

glucagon

Hormone secreted by alpha cells to increase blood glucose.

insulin

Hormone secreted by beta cells to decrease blood glucose.

glycogen

Storage form of glucose in liver and muscles.

facilitated diffusion

Transport across membranes via carrier proteins (GLUT).

secondary active transport

Transport using energy from an ion gradient (SGLT).

GLUT transporters

Facilitate glucose diffusion across membranes, insulin-dependent in some tissues.

SGLT transporters

Use sodium gradient to reabsorb glucose in kidneys; insulin-independent.

filtrate

Fluid filtered by kidneys from blood.

saturation

Maximum transport rate when all carrier binding sites are filled.

homeostasis

Maintenance of a dynamically stable internal environment necessary for cell health.

negative feedback

A mechanism that counters changes, restoring a regulated variable toward its setpoint.

positive feedback

A mechanism that amplifies changes, moving a variable further from its setpoint.

feedforward control

A response made in anticipation of a change, before it occurs.

tonic control

Single controller regulates a parameter in an up/down fashion (e.g., blood vessel diameter).

glycogenolysis

Breakdown of glycogen into glucose.

diabetes mellitus

A disease causing abnormal insulin secretion or responsiveness, leading to hyperglycemia.

complications of chronic hyperglycemia

Cardiovascular disease, kidney failure, nerve damage, eye vessel damage, blindness.

glucosuria

Glucose in urine due to exceeding SGLT transport maximum.

polyuria

Excessive urination caused by osmotic effect of glucose in urine.

polydipsia

Excessive thirst caused by dehydration from polyuria.

stress hyperglycemia

Temporary elevation of blood glucose during illness or stress due to reduced insulin and mobilized glucose.

causes of hypoglycemia

Medications, alcohol, liver/heart/kidney disorders, or hyperinsulinemia.

symptoms of hypoglycemia

Weakness, tremors, hunger, irritability.

oral glucose tolerance test (OGTT)

The body's ability to respond to excess glucose ingestion.

glucose dose used in OGTT

75 grams glucose solution (10 oz).

fasting before OGTT

8-16 hours clinically; in lab, at least 2 hours without food/drink (except water).

normal fasting glucose levels

70-110 mg/dl.

fasting glucose indicating diabetes

≥126 mg/dl.

2-hour post-glucose level indicating diabetes

>200 mg/dl.

2-hour post-glucose level indicating impaired tolerance

140-199 mg/dl.

equipment used in OGTT lab

75g glucose solution, glucometer & test strips, lancing device, alcohol wipes, band-aids, gauze, biohazard container, Diastix strips.

first step in OGTT in lab

Measure fasting blood glucose and urine glucose.

blood and urine glucose testing frequency after ingestion

Every 30 minutes for 90 minutes.

function of a glucometer

Measures blood glucose concentration using a test strip and a small blood sample.

how to use a glucometer

Insert strip, prick finger, apply blood to strip, wait for reading, record result.

purpose of Diastix strips

To detect glucose in urine using a color-sensitive chemical pad.

transport used by GLUT proteins

Facilitated diffusion.

transport used by SGLT proteins

Secondary active transport, driven by sodium gradient.

maintains Na+ gradient for SGLT

Na+/K+ ATPase (primary active transport).

GLUT transporters insulin dependency

Some are (e.g., GLUT4 in muscle/adipose), while others are not.

SGLT transporters insulin dependency

No, they reabsorb glucose in the kidney independent of insulin.

importance of OGTT in medicine

It helps diagnose diabetes and impaired glucose tolerance.

most important value in simple diabetes screening

The 2-hour post-glucose sample.

factors affecting OGTT results

Food, exercise, stress, and certain medications.