Week 35: Kidney Function - Waste Management System

Renal System Maturation

Week 35 marks the near-completion of your baby's kidney development, with the renal system now capable of the complex task of filtering blood and producing urine. Your baby's kidneys have been functioning for months, but they're now sophisticated enough to handle the increased metabolic demands of life outside the womb.

The kidneys perform numerous crucial functions beyond simple waste elimination, including:

• Regulating fluid and electrolyte balance

• Controlling blood pressure through hormone production

• Maintaining acid-base balance in the blood

• Producing hormones that stimulate red blood cell production

• Filtering toxins and waste products from the blood

Nephron Development Complete

The functional units of the kidneys, called nephrons, are now fully formed. Each kidney contains approximately 1 million nephrons, and remarkably, no new nephrons are formed after birth. This means that the nephrons developing now must last your child's entire lifetime.

Each nephron consists of:

• A glomerulus (filtering unit)

• Bowman's capsule (collection cup)

• Tubules for reabsorption and secretion

• Collecting ducts for final urine concentration

The sophisticated structure of nephrons allows for precise control of what substances are retained or eliminated from the body.

Urine Production and Amniotic Fluid

Your baby is now producing significant amounts of urine – up to 500ml per day. This urine becomes part of the amniotic fluid in a continuous cycle where your baby swallows amniotic fluid, processes it through their kidneys, and produces more urine. This cycle is crucial for:

• Maintaining proper amniotic fluid levels

• Developing the digestive system through swallowing practice

• Exercising the kidneys and urinary system

• Contributing to lung development as amniotic fluid is "breathed" in and out

Concentrating Ability Develops

One of the most sophisticated kidney functions – the ability to concentrate urine to conserve water – is beginning to develop. This function is controlled by antidiuretic hormone (ADH) and requires mature tubular function. While not fully developed until after birth, the foundation for this crucial water conservation ability is being established.

Electrolyte Regulation

Your baby's kidneys are learning to regulate important electrolytes like sodium, potassium, and calcium. This regulation is crucial for:

• Proper muscle and nerve function

• Maintaining blood pressure

• Supporting bone development

• Ensuring proper cellular function

The ability to maintain electrolyte balance is essential for survival and will become even more important after birth when your baby is no longer receiving these substances directly from you.

Blood Pressure Regulation

The kidneys play a crucial role in blood pressure regulation through the renin-angiotensin system. Your baby's kidneys are beginning to produce renin, an enzyme that helps control blood pressure and blood volume. This system won't be fully mature until after birth but is essential for cardiovascular health.

Your Baby's Overall Development

Your baby now weighs approximately 2.4 kilograms (5.3 pounds) and is gaining about 200 grams per week. Most organs are now mature enough to function outside the womb, though continued development will improve efficiency and reduce the risk of complications.

The immune system is also maturing, with your baby receiving increasing amounts of protective antibodies from you through the placenta.

Recipe: Kidney-Supporting Cranberry Quinoa Bowl

Ingredients

• 1 cup cooked quinoa

• 1/4 cup dried cranberries

• 1/4 cup chopped walnuts

• 2 cups baby spinach

• 1/4 cup crumbled goat cheese

• 2 tbsp olive oil

• 1 tbsp balsamic vinegar

• 1 tsp Dijon mustard

• 1 tsp honey

• Salt and pepper to taste

Instructions

1. Massage spinach with a pinch of salt until wilted

2. Add quinoa, cranberries, and walnuts

3. Whisk together olive oil, vinegar, mustard, and honey

4. Toss salad with dressing and top with goat cheese

5. Cranberries support urinary tract health

Sources:

1. Rodriguez-Soriano, J. (2019). “Renal tubular acidosis: the clinical entity”

2. Hinchliffe, S.A., et al. (1991). “The effect of intrauterine growth retardation on the development of renal nephrons”

3. Beall, M.H., et al. (2007). “Regulation of amniotic fluid volume”