Digestion and Absorption
What are the principle components of the digestive system?
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Pancreas
Liver
Gall Bladder
Why can't humans live without water?
Water is the basic substance for all metabolic processes in the body
Water regulates body temperature
Water enables transport of substances essential for growth
Water allows for the exchange of nutrients and metabolic end products
Water is also a good lubricant for joints, tendons and muscles
Define the term basal metabolic rate [BMR]
BMR is the amount of energy expended while at rest in a neutrally temperate environment in a post-absorptive state (the digestive system is inactive, requiring 12 hours of fasting)
State the approximate glycogen content of specific skeletal muscle fibre types
Type 1 - low
Type 2a - mid
Type 2b - high
Draw a Nephron.
Following elements included:
o Glomerulus
o Bowman’s capsule
o Loop of Henlé
o Collecting duct
State the pH range of various areas of the digestive system.
Mouth - 5.5 - 7.5
Stomach - 1 - 4
Small Intestine - 6 - 8
State where extracellular fluid can be located throughout the body!
o Blood plasma and lymph
o Saliva
o Fluid in the eyes
o Fluid secreted by glands and the digestive system
o Fluid surrounding the nerves and spinal cord
o Fluid secreted from the skin and kidneys
State the components of daily energy expenditure
Basal metabolic rate
Thermic effect of physical activity (exercise)
Thermic effect of feeding (eating)
Define the term glycemic index.
Glycemic index (GI) is the ranking system for carbohydrates based on the immediate effect of the food on blood glucose concentrations when compared with a reference food such as pure glucose.
What is the purpose of a kidney?
The kidney controls the retention and loss of water through its nephrons
o A nephron is the basic structural and functional unit of the kidney
The nephrons are responsible for:
o Regulating the concentration of water and soluble substances by filtering blood
o Reabsorbing what is needed in the body and excreting the rest as urine
o Eliminating waste from the body, regulating blood volume and pressure, controlling levels of electrolytes and metabolites, and regulating blood pH
Describe the function of enzymes throughout the digestive process! Why are they needed?
If you exclusively talked about specific enzymes without connecting them to the larger context of why they are needed you are awarded no points and you successfully made your teacher cry!
Enzymes catalyze chemical reactions in the body that are otherwise very slow (e.g. catabolism of macronutrients)
Enzymes achieve this by providing a shorter alternate reaction pathway for reactants into products
The rate of reaction is increased, as this alternate pathway has a lower activation energy
Enzymes are proteins themselves, thus their activity is highest under optimum conditions of temperature and pH
Enzyme activity increases with temperature until around 37°C (normal body temperature)
Temperatures above 37°C lead to a decrease in activity as the enzyme begins to denature
The optimum environment for enzyme activity is provided/maintained by the digestive tract
Each macronutrient requires a specific enzyme, which is produced in particular areas of the digestive tract
Without enzymes, digestion would be a long and inefficient process, with energy not being supplied at an appropriate rate
Discuss the regulation of electrolyte balance during acute and chronic exercise.
The electrolytes present in the human body include:
o Sodium
o Potassium
o Calcium
o Bicarbonate
o Magnesium
o Chloride
o Phosphate
Electrolytes are a component of blood plasma
Electrolytes are essential for normal cell metabolism and it is essential for them to be balanced within the blood plasma
Electrolyte balance is regulated by the kidneys
Acute exercise:
o This is short duration exercise
o Acute exercise does not require electrolyte replacement after being lost in sweat
o Diluted sports drinks are adequate to replace lost electrolytes in acute exercise
Chronic exercise:
o This is long duration, medium-high intensity exercise
o Exercise longer than an hour requires electrolyte replacement
o For chronic exercise, it is important to actively replace lost sodium
o However, consumption of excess plain water can cause sodium depletion and may lead to hyponatremia
Discuss the association between body composition and athletic performance. Be sure to include a discussion of fat mass, lean mass and fat free mass.
Fat Mass (FM) – The mass of all lipids in the body that can be extracted
Fat-Free Mass (FFM) – The mass of all remaining tissues and materials in the body including fluids (i.e. total body mass excluding FM)
Lean body mass – Includes combined weight of muscles, bones, ligaments, tendons and internal organs
Differs from FFM as it includes a small percentage of essential fats in bone marrow and organs, also it excludes fluids
Lean muscle mass – The pure muscle mass without fat
Low body fat is important for:
o Weight-bearing endurance sports (e.g. marathon)
o Anti-gravity sports (e.g. long jump)
o Aesthetic sports (e.g. gymnastics)
Whereas higher body fat is important for:
o Power sports (shotput)
o Contact sports (rugby)
Fat is required for:
o Shock absorption (rugby)
o Buoyancy (swimming)
o Thermal insulation (ocean swimming)
o Fuel stores (cross-country skiing)
Discuss the use of nutritional ergogenic aids in sports.
Bring in a discussion on:
Sports Drinks, Caffeine, Creatine and bicarbonate
o This is the tubule that connects the proximal tubule to the distal tubule
o The main function of this structure is to allow the body to reabsorb water and electrolytes (Sodium Chloride) from the urine
o When fluid moves down the descending limb of the loop water is filtered out due to this portion’s high permeability to water
o When fluid moves up the ascending limb of the loop, sodium chloride is actively transported out due to the high permeability to electrolytes in this portion
o This causes the medulla to become hypertonic (salty) as the sodium chloride is actively transported from this area
o Since the medulla is hypertonic, this causes water to follow its concentration gradient and transport into the medulla by diffusion when the permeability increases (as in the descending tube)
What is the loop of Henle?
TO THE BOARD!!!! You and your team must create a table of the enzymes that we studied throughout this course. In your table include the following:
Enzyme Name
Enzyme Function
Area of Enzymatic Activity
Pepsin - Breaks proteins into smaller peptide chains - in the stomach
Pancreatic Amylase - breaks starches into disaccharides - small intestine
Sucrase - breaks sucrose into glucose and fructose - small intestine
Lactase - breaks lactose into glucose and galactose - small intestine
Maltase - breaks maltose into two glucose - small intestine
Trypsin - breaks peptide chains into smaller peptide chains
Peptidase - breaks small peptide chains into amino acids - small intestine
Lipase - breaks lipids into fatty acids and glycerols - small intestine
Describe how the hydration status of athletes can be monitored.
Monitoring hydration can be based on:
o Urine color – A darker color suggests a higher level of dehydration
o Urine osmolarity – The amount of solute per unit of volume (i.e. the concentration of urine) higher levels suggest greater levels of dehydration
o Variation in body mass loss – The mass of the athlete before compared to after the event
Discuss dietary practices employed by athletes to manipulate body composition. Give the general formula for energy balance in your response.
Gaining muscle mass (increasing FFM):
o Strength training can cause muscle hypertrophy
o To facilitate this adequate protein intake must be consumed
o However, changes in body composition occur over the long run
o There are also risks associated with excess protein intake relating to damaging the kidneys
Reducing fat mass (FM):
o Low energy intake causes the body to metabolize fat stores, thus reducing FM
o This method is associated with lean athletes
o However, there are risks associated with losing excessive levels of body fat, which can prevent the normal functioning of the body
Dehydration:
o As water takes up a large percentage of body mass, athletes may deliberately restrict fluid intake in order to decrease weight
o E.g. Boxers, Judo and Jockeying
o However, there are risks associated with damaging the cardiorespiratory system
Diets:
o High protein diets, like the Atkins diet are used to synthesize amino acids, thus increasing FFM
o Diet pills, fad diets and crash diets may be beneficial for short-term weight loss, but not long-term
o Note: Higher-intensity sports require greater glucose intake
• An athlete’s nutrition plan should be individualised to meet their needs of training and competition
State the reasons for adding sodium and carbohydrate to water for the endurance athlete
Sodium:
o Stimulates thirst receptors, increasing the athletes urge to drink, therefore increasing hydration
o Reduces urine production
o It is the major electrolyte in extracellular fluid and so replenishes lost electrolytes (mostly through sweat), thus maintaining blood plasma osmolarity
o Can help with the absorption of carbohydrates
Carbohydrate:
o Stimulates fluid uptake by lumen
o Replaces glycogen stores in skeletal muscle and the liver (lasts around 60-90 minutes)
o It isn’t too concentrated (which can inhibit hydration)
These can be provided by sports drinks, bars and gels
Describe the pathway fluid takes through a Nephron. Include a discussion on where water and electrolytes are reabsorbed.
Thorough and accurate discussion provided.
!!!!!!!!!!!!!!!!!!!!DAILY DOUBLE!!!!!!!!!!!!!!!!!!!!!!!
For 1000 points... Describe the absorption of glucose, amino acids and fatty acids from the intestinal lumen to the capillary network!!!!!! Woo!
Glucose:
- Carbohydrates are absorbed in the small intestine in the form of the monosaccharide glucose
- Glucose is first transported into the epithelial cells of the villi by active transport
- Then glucose is actively transported across the brush-border membrane found on the villi and microvilli
- Next, the glucose passes through the cytosol of the absorptive cell
- Finally, through facilitated diffusion the glucose crosses the basolateral membrane and enters the capillary network before being used in the body
Amino acids:
- The mechanism by which amino acids are absorbed is almost identical to that of glucose
- The only significant difference is that amino acids cross the basolateral membrane through active transport instead of facilitated diffusion
- Amino acids cross the brush-border membrane through active transport, pass through the cytosol of the absorptive cell and cross the basolateral membrane through active transport, before entering the capillary network
Fatty acids:
- Lipids undergo a slightly different process as they are insoluble in water
- Triglycerides are too big to be transported across the brush-border membrane and so must first undergo digestion via lipase
- Once the fatty acids and glycerol diffuse through the brush-border membrane and are inside the cytosol of the absorptive cell they are rebuilt into triglycerides
- The triglycerides then cross the basolateral membrane through diffusion into the lymphatic system
- Finally, the triglycerides leave the lymphatic system and enter the blood stream near the heart
Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms - USE AN EXAMPLE RELATING TO WATER IN YOUR RESPONSE!
Homeostasis – The maintenance of a constant environment where levels and concentrations of the body are in an ideal range
Negative feedback – The mechanism of response where a stimulus initiates actions that reverse/reduce the intensity of the original stimulus
Negative feedback is used to keep the internal environment between limits:
o It uses the nervous and endocrine systems
o It has a stabilizing effect as any change from a set point level will result in an opposite change
o However, negative feedback is only triggered when there are significant increases or decreases from the set point
• An example is the loss of blood plasma through sweat:
o This is detected by the hypothalamus, which responds in two ways; gain and retain
§ Activates a thirst sensation (desire to drink; i.e. gain)
§ The pituitary gland also secretes anti-diuretic hormone (ADH), which increases the permeability of the collecting ducts and renal tubes, causing them to retain fluid (osmosis) and decrease urine production (i.e. retain)
This decreases the amount of water absorbed by the kidneys and thus decreases urine production
This mechanism results in an increased H2O availability in extra-cellular fluids (ECF’s)
When this H2O availability reaches the ideal point again, the hypothalamus detects this and
responds by:
§ Deactivating thirst
§ Reducing the secretion of ADH
o Thus, this process shows how negative feedback mechanisms maintain homeostasis as an action is initiated to reverse/reduce the loss of body fluid
Please write a diet and exercise plan (1 month) for an athlete who is attempting to increase their lean mass for rugby.
Diet - high in protein and fat, lower in carbohydrates accept any relevant examples
Exercise plan - detailed and specific to the needs of rugby
Explain the relevance of GI with regard to carbohydrate consumption by athletes pre- and post-competition - discuss what an athlete should consume before, during and after an endurance event. Provide reasoning for your selections.
• Low GI foods are digested slowly à They can remain in the small intestine for hours after competition
o This is beneficial for athletes as they provide a slow and sustained release of glucose that occurs even during exercise
o Carbohydrates with a low GI also provide long term health benefits and may prevent diseases such as diabetes, obesity and heart disease
• High GI foods may assist in speeding up glycogen replenishment after a bout of activity
o Carbohydrate rich, high GI foods may also aid in refueling prior to future training or competition
• Athletes should aim to lower the overall GI of their diet by shifting their choice towards consuming more low GI foods
o Usually an athlete will consume less fat on a lower GI diet as they are less hungry
• Pre-competition:
o The recommended carbohydrate consumption of an athlete prior to competition varies mostly based on the type of activity
o Events that are of a shorter duration and utilize the anaerobic system may benefit from the consumption of higher GI foods
§ This is because high GI foods provide a rapid release of glucose into the bloodstream, which is beneficial for shorter events
o On the other hand, events that are of a longer duration and utilize the aerobic system will benefit from the consumption of lower GI foods
§ Lower GI foods will be beneficial prior to exercise as they slow the rate of glucose absorption in the blood, thus eliminating the insulin surge
o Finally, athletes must also ensure to not foods that cause cramps or flatulence pre-competition
• Post-event:
o Skeletal muscles are more sensitive to glucose in the first hour after exercise, Thus large amounts of high GI foods should be consumed in this period
o This should be accompanied by rest to speed up glycogen replenishment
o Optimal conditions give glycogen replacement at approximately 5%/hour
Congrats - if this is not the last question picked, the team who picked it gets a free 500 points.
You win. Or maybe you waited too long to challenge yourself and you lose.